TI 58/59 ROM modules and OP instructions

[Gene]

I don't know, but if there is an answer, it should lie in the PDF copies of the TI PPC Notes through their 14 year history.

What? You don't have these PDF copies? They can be found here:

TI PPC Notes


As another guess, sometimes factory software has to be written very early in the development life of the calculator (which is one reason it is so often so bad!)... perhaps the development finalization of the OP code structures wasn't early enough to be reliably used in the library modules?

I don't know.