I've got an archive of installers going back to Yosemite...not sure why, and I assume that the procedure outlined by V1 in Sierra and High Sierra installers now say "damaged will work should I ever need to run one with an expired certificate.
And on the other hand, maybe I'll d/l the fresh ones all the same.
The new Great Equalizer is the SEND button.
In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire