It is not clear to me if the codes in question are actually copyrighted.
Probably so if they appeared in publications displaying the copyright notice.

As long as GE properly supports any older systems that use the codes,
then I have no problem with such legal-shmegal.

However sometimes if a company stops supporting a particular product
and refuses to supply even the access codes so the users can at least
perform the support themselves on a particular system, then they
would not have much of an ethical leg to stand on and the copyright
could then be effectively 'busted' in court.

Current General Copyright rules (found on the net):

Copyrighted 1964-1977
All books initially copyrighted in the US from 1964 through 1977 have had their copyrights automatically renewed (by law) and the copyrights are still in force. The initial copyright term was 28 years; the renewal was for 67 more years. So a book initially copyrighted in 1964 will pass into the public domain in 1964 + 28 + 67 + 1= 2060.

Copyrighted 1978-
All books initially copyrighted in the US from 1978 to date are still protected by copyright law. The period of copyright protection is governed by complex rules. Generally speaking copyright protection ends 70 years after death of author.