You cannot draw any conclusions from this similarity alone. The scheme is common and sequential numbers were likely used in many other legitimate cases. You think this is a flop only because The Insider has found very close numbers of passports for people in the same military unit. But there are just 4 numbers of 100 in the same range. Is there any evidence that the remaining people belong to the same unit, are spies or even work for Russian government?

Sure, but that's no different back then than now?

You catch 3 spies in 1950. Someone shuffling through their paper files notices the numbers are close in range. You have a suspected 4th, and interestingly the passport number is clustered with the prior 3.

You use a super computer to analyze passport numbers and compare them to 3 known spies. The computer spits out a pattern. [...] You have a suspected 4th, and interestingly the passport number is clustered with the prior 3.

As per the original post it "is part of a numerical range reserved exclusively for members of Unit 29155".

I could see if it wasn't a numerical range, but rather a reserved pattern (e.g. the 2nd, 3rd, 7th, 8th numbers were always sequential), then sure, a super computer could help you analyze known number to find a pattern. But it's just a group of number close in series? That seems discoverable by mere humans.

In WWII serial number analysis was used to estimate Nazi tank production rates. That sort of analysis was old had long ago now. Somehow no one in Russia seems to remember.

I doubt that. It is more likely that it is not considered a significant risk compared to everything else. How exactly is this information useful to adversaries? It certainly won’t help uncovering illegals, because their passports are kept away from Western databases. It doesn’t help to block spy operations, because you can connect passport numbers to specific actions only after they happened or you used other methods to detect spies. It doesn’t help breaking plausible deniability to blame Russian government officially, because you would need the hard evidence. So what’s the point in protecting this information more?

> because their passports are kept away from Western databases.

Except unless they get arrested in the West and their secret passports fall into Western intelligence hands.

> It doesn’t help to block spy operations, because you can connect passport numbers to specific actions only after they happened

But getting caught must be no fun.

> It doesn’t help breaking plausible deniability to blame Russian government officially, because you would need the hard evidence.

Nonsense. A block of sequential passport numbers for supposedly unrelated people you suspect of being spies is evidence plenty hard enough.