If I understand your comments correctly (which I strongly suspect I haven't), I shouldn't have been able to restore/recover my system (10.7.5) and everything else from Time Machine (sans Recovery HD) the way I did.
You should indeed be able to restore. TM backs up Recovery HD in a manner that allows you to boot into it, and from there you can restore. You can even restore from the very same TM backup, if you want.
However, the only thing that didn't get recovered was the HD Recovery partition.
That is correct. TM backs up (almost) everything on your boot volume (and any other volumes you tell it to back up). It also backs up your Recovery HD, but backs it up in a different way, because Recovery HD is not
on your boot volume. If you have one, it's a separate partition on the same disk.
As described earlier, I had to start up using HD Recovery from the thumb drive to access Time Machine and then restored everything from the last backup. There were no other options I could find and no other way to access Time Machine.
Right. When booted into Recovery HD, you have several options (install, Disk Utility, Safari, etc.), but the only TM-related option is to do a full-disk restore to a partition of your choosing.
You have exactly these same options whether you booted into the Recovery HD partition on your main drive (if you have one), the Recovery HD partition on your thumb drive, or the TM backup of Recovery HD. They're all exactly the same.
I just tried the 'option' option which did take me to TM's hard drive. As far as I can see, I made all the appropriate choices when restoring my hard drive back in October. So if Recovery HD was backed up, I can see no way of accessing it.
You just did "access" it, by booting into it.
Recovery HD is not a file on your boot volume. It isn't even on your boot volume. It's a separate partition, on the same disk as the boot volume, but next to it, not inside it.
That partition is created by the installer, so you don't get one without running the installer. For this purpose, a full disk restore doesn't count as an install.
TM backs it up anyway, even though it's not a file, but not the way it backs up ordinary files. Oddly enough, though, the backup it makes
is a file, not a partition, so
diskutil can't see it. But the file isn't saved where your other files are saved, so you can't find it by browsing either.
You can use it, though, by booting into it. This is no different than the "real" Recovery HD: you can boot into it, but you cannot otherwise see it. (The
diskutil shell command will show it to you, but that's all it does: show it to you. In like vein, you can see but not otherwise use the copy on your Time Machine backup. It's at /Volumes/"
disk_name"/Backups.backupdb/.RecoverySets/0/com.apple.recovery.boot. Note that .RecoverySets starts with a period, making that folder invisible.)
So, back to the original query: Is there any way I can put a Recovery HD partition on my hard drive from the Recovery HD on my thumb drive?
There is. One way is to reinstall (not restore) the OS on the boot volume. Unless you had the foresight to save off a copy of the installer itself, you'll need to download it again. It's 3.76GB, which is perhaps more than you're willing to download. The installer is an application named "Install Mac OS X Lion.app". The installer is not your Recovery HD, which is only 650 MB.
There is another way, but it involves serious Terminal work. If you'll pardon me saying so, it's way above your abilities. (The steps would be to use the
diskutil command to carve out a 650MB partition from the end of your boot partition, use the
dd command to clone the Recovery HD partition from your thumb drive onto it, and finally set the partition kind of the new partition to "Apple_Boot".)
You may want to google for a pre-built script to do it. I'm sure there are some. I'll leave the googling to you. Be sure you have a backup. Preferably at least two.
Your comment that "the Time Machine backup volume shows up as a bootable partition if you hold down the option key while starting up, and selecting it boots you into the backed-up recovery partition" is what I really don't understand.
I interpret it as: With no thumb drive connected and only my backup hard drive containing TM backups I should start the iMac by holding down the option key. If so, I could always go back and try to do another restore if that indeed would put Recovery HD on the hard drive.
You understand almost perfectly. You have it exactly right, right up until the last clause of the last sentence. A restore is not an install. Only the installer creates a Recovery HD partition.
But you don't need one, as long as you've got your TM backup. Booting into the TM volume is functionally the same as booting into a "real" Recovery HD. Or, you can boot off the thumb drive, which again is functionally the same.
The Recovery HD partition contains a compressed image of the recovery software. (The partition is 650MB, but it's not full. The compressed image that is the guts of it is only about 450MB.) When you boot into it, the first thing it does is decompress that image into RAM, and then re-boots off the expanded image. Internet Recovery works exactly the same, except that the compressed image is downloaded instead of being read from disk.
Once the recovery software is expanded into RAM, it makes no difference where the compressed image came from. At that point, you're booted into a RAM disk, and can safely remove whatever drive (boot, TM, thumb, internet) the software came from.
But you will need internet access to get the installer. The entire Recovery HD partition is only 650 MB in size. There's no way a 3.76 GB installer can fit. (Compression won't help. The installer has already been compressed to within an inch of its life to bring it down to "only" 3.76 GB.)
Unless, as I said, you had the foresight to squirrel away a copy of the installer.
I am very reluctant to start futzing around with what I've got, since everything is working hunkydory without the Recovery HD installed but being accessible via the thumb drive.
I'm of two minds about this. Recovery procedures should be practiced, so you won't panic when you really need them. On the other hand, if it ain't broke, don't fix it. I think the latter is the better choice at this point. After all, you have done at least one full-disk restore. That's probably enough practice.
I'm also stymied by your "installer" comments. (If restoring my OS and files didn't "install" them, then we're speaking different languages.)
I had noticed that "speaking different languages" part. A "restore" puts back files you previously had; an "install" can create new files, even files you've never had. There's no reason a full-disk restore couldn't re-recreate the Recovery HD partition. I assume Apple chose not to do so because they figure you've already got one on the TM partition.
I'm not sure I'm in total agreement with that. You have a backup of "Recovery HD" on your TM backup, but only because at some time after 10.7.2 you did a TM backup at a time when you also had a Recovery HD partition for it to copy. If you ever have to wipe your TM backup and start fresh, it'll never see a Recovery HD and won't back it up. You new TM archive will not be bootable. You'll need the thumb drive then.
With a naked hard drive and no thumb drive, nothing would happen, so I don't see how holding down the option key would achieve anything.
With a naked hard drive and no thumb drive
and no TM backup that has ever seen "Recovery HD", nothing will happen when you hold down the option key.
In the same situation but with a TM backup that has never seen "Recovery HD", you can hold down ⌘R to get into Internet Recovery mode. Let it download the recovery software ("only" 450 MB or so), and use that to do a full-disk restore from TM. 450 MB is a lot smaller than 3.76 GB for the installer.
In the same situation but with no TM backup at all, you're SOL anyway.