Okay, here's a head-scratcher and no mistake.

I have a 15" 2016 Macbook Pro (a Macbook Pro 13,3). A long time ago, I ran a firmware update on this Mac. All well and good. The Mac came with Firmware version 428.0.0.0.0 and the current version from Apple is 429.60.3.0.0.

The Mac went in last year for warranty service, and they replaced the logic board. The logic board they put in is back to Firmware 428.0.0.0.0, the old version.

But here's the thing: I can't update to the new version! App Store doesn't see it as an update. It can't be installed, I suspect because somehow the update logs or something "remember" that I've already run the update. And without the firmware update, I can't upgrade past macOS High Sierra (the 429.60.3.0.0 firmware is required for any operating systems beyond High Sierra).

It's a real pickle. I can't find a standalone firmware updater anywhere, not even on my Apple Developer account. Any ideas?

The first thing I"d try is searching /Library/Receipts/InstallHistory.plist for the applicable one - if, in fact, there is one - and deleting it to see if it triggers the App Store.

Failing that, Apple owes you.

They didn't do a complete job of replacing the logic board and owe you either a new board or, at the least, the update.

How far away is the Apple Store?

I had a similar thing occur with a previous iMac. The solution is to return to the Apple Store. When it happened to me and I returned the person said something like "Oops, Service forgot to finalize the installation." They were able to do it on the spot, using secret software, of course, and all was good.

That's an excellent idea. Alas, the nearest Apple store is about 45 minutes away.

Aw, that's nuttin'....for me it's nearly three hours away! (Probably the same store.....)