Many of the Soviet maps are compilations form local/colonial series. The
Russians didn't do their own surveying but reproduced colonial (often
British) surveys. Thus the Russian sheets for many countries are often
incomplete and dated in their coverage, and boundary information may be
quite inaccurate. The Brits did a 100k series of UAE in the 60s which the
Russians appear to have copied for their UAE series. Likewise the Russian
200k maps of northern Bangladesh are based on the British 4" series (253k)
of the colonial period (and the US AMS series of the area, which in turn
was based on the British maps). The boundary the Russian draw at Cooch
Behar is a straight line in places when in fact as we know it is quite
wiggly. You must read the compilation notes on a map to determine the true
age and source of the data used. A 1980s map may be based on 1930s
information, with only minor amendments. Caveat lector.

Russian maps are a good source for Russian regions, but for other regions
their main advantage is their standardised style, not their up-to-datedness.

Brendan