This is the holy grail. The PDF is the one scanned from the Dover 1993 edition. How to recognize the verified version: It has 309 pages, and the solution to Problem 1 is a geometric proof involving a square and a triangle. Unverified copies miss Diagram 3 on page 12.
These can be legally accessed through university math libraries or MCCME’s digital archive. russian math olympiad problems and solutions pdf verified
https://www.math.ucla.edu/~robjohn/math/ussr_olympiads.pdf (UCLA archive) This is the holy grail
Since the originals are in Russian, verified PDFs ensure that nuances (like "non-negative" vs. "positive") aren't lost in translation. Top Resources for Verified Problems and Solutions russian math olympiad problems and solutions pdf verified