HP 87: PLOT ROM B 00087-60929

[Michael Fehlhammer]

My recently acquired HP 86B is equipped with a version of the plotter rom I never have heard of.
A case of an HP 00087-15002 Version B module has a sticker on it, overwriting the original label and saying:
00087-60929 PLOT ROM B.

Google doesn't find anything related to the given product number.
Maybe this plotter rom was released very late in the life cycle of the 86B, to support some new plotter models? That would explain that it is so rare. But I'm just guessing.
Does anyone know anything about that rom module?