This might be a dumb question, but what is the difference between the two, posp, and pso???

Quoted: This might be a dumb question, but what is the difference between the two, posp, and pso???

This site seems to use the two interchangably.

I actually spent a while trying to make sense of this.

I think the POSP designation is only used by the Belorussian BeLOMO plant (aka Zenit) in Minsk but they also use PO for some scopes.

PSO scopes seem to be made by Novosibirsk Instrument-making Plant  but they also use the PO designation for "civilian" models.

And there are also many other Russian optics manufacturers, so the above may be completely wrong hereZagorsk Optical and Mechanical Plant that at least earlier made "PPO" or "Kronos" scopes.
There's also a VOMZ (Vologda optical-mechanical plant) that also at least has at some opint in time made rifle scopes that were called Pilad.

At the Novosibirsk plant's page I noticed a 2.5x18 PO scope but there was no pic. Anyone seen this anywhere?