Trying to find out what they used to mean would be almost impossible, many of the publishers don't exist anymore and, even if they do, are unlikely to have records stretching back too far (keep in mind everything was on paper then, and usually done locally...much of that information is gone for good). Not to mention there are older editions and works that had no ID numbers of any kind (I have quite a few myself...they just have the date/publisher name/location).

In terms of converting them, basically it would be guesswork. It's like using old recipes that have measurements like 'drab'...there's no Rosetta stone to say what a drab was in comparison to modern measurements...we just have little clues here and there and take our best, educated guess...but we could be miles off and never know it.

Sorry I can't be more help.