That’s possible. But those underground facilities (established with the idea of surviving nuclear war) at the steel plant were designed and constructed (as best as I know from limited reading) during the times when the Soviet Union was a CENTRALIZED top down command economy. My suspicion is that somewhere in the former Soviet Union’s successor states (most likely Russia) there was centralized information on ALL of the Soviet Union’s major underground nuclear shelters. Of course, that’s only my conjecture. And it’s always possible that upon the dissolution of the Soviet Union entropy set in and such important information degraded or was discarded.
There was no internet back in 1991 either. So it's not like the Soviets could have uploaded it to a website somewhere.
Or even a floppy disk, in this case.