It really had nothing to do with the period of time the fonts were released over. After all, even if they were all available at once wouldn't mean that users would buy them all at once. Also, the symbol characters were just an additional complication; even without them we couldn't
guarantee there would not be reflow. So we made the decision that we were going to have to rename the fonts. It was a tough call, and debated heavily at the time.
Keep in mind also that if the names are the same, there are compatibility problems going in the other direction. You do a nice document in InDesign using small caps and oldstyle figures in the OpenType version of Glurbish Modern. Then you pass it on to your colleague who is using the old Type 1 version. Because the extra goodies are in separate fonts in that version, your small caps turn into lower case, your oldstyle figures turn into lining figures, and by the way, that euro symbol you used disappears entirely when she opens the document. Oh, and if she's on Windows, she doesn't have Symbol substitution, so any of those characters also disappear - even though maybe you were on Windows as well. It's not just a matter of the metrics changing and getting reflow.
Anyway, after we made that decision, we were free to enhance the fonts even further. So we did a bunch of things, from adding not only the euro but also the litre and estimated symbols (not present in the Type 1 versions), to enhancing the kerning of the accented characters (which was very lacking in some of the oldest Type 1 designs).
Regards,
T