I spent some time comparing the 1926 map and the 1927 list. Turns out there are a few significant differences, most of which were in - you guessed it - Pennsylvania. And based on the FHWA article NE2 linked to upthread, this was undoubtedly a result of Pennsylvania's late objections and revisions.
So, for this thread: US 622 and 711 were both shown on the 1926 map. But by the time of the 1927 list, all of US 622 had been replaced by an extension of US 522, and all of US 711 had been replaced by a rerouting of US 220. And my understanding is that Penn. didn't even signpost US routes until 1928. So if that's true, then probably no 622 or 711 shields were ever manufactured. Thoughts?