Yes those Soviet era maps were military and classified.
They only ended up in popular circulation after a quick retreat, fuckup and corruption that happened when the Soviet forced retreated from the Baltic states.
I've heard even US militaryused(uses?) some of those maps for parts of Africa or used then initially in Afghanistan. As nobody else has bothered much to go and cross reference and built detailed maps of those regions in that much detail.
> Worse, the maps for the masses were deliberately distorted with a special projection that introduced random variations. “The main goal was to crush the contents of maps so it would be impossible to recreate the real geography of a place from the map,” Postnikov tells me. Well-known landmarks like rivers and towns were depicted, but the coordinates, directions, and distances were all off, making them useless for navigation or military planning, should they fall into enemy hands. The cartographer who devised this devious scheme was awarded the State Prize by Stalin.