My macro capable camera has stolen thus I tried to depict the logo rather giving a photo. But I will post a photo anyway.
There is no date mark. There is a "n" just nearby logo. It is probably 20 years old maybe even older. It is hard to find info about East European, Soviet era semiconductor products also. I suspect that my BC500's fall into this category. I'm updating the logo.
You need to ask around on a German or Hungarian website. That would check your theory that they are Soviet block production pre 1989. The only analog website I know of is the german analog organ website.