I think the difference is probably in the fact that Poland was a USSR satellite nation, much like DDR, while in Latvia after occupation they didn't set up a pup

I think the difference is probably in the fact that Poland was a USSR satellite nation, much like DDR, while in Latvia after occupation they didn't set up a puppet state, but directly integrated us into the USSR. The implication here is that the regime secret services in Latvia not just collaborated extensively with Moscow, but were in fact part of the same organization. Meaning, that it is very likely that there existed instructions for emergency situations in which the most sensitive documentation needs to be shipped to Moscow.