Yes, I do, That was subsequently determined by WE Engineers to have been an unintentional mistake.
Also, another undocumented feature on both the 1 and 1A ESS was that call waiting would work during a three-way call. This was carried over to the 5ESS, but later dropped. The DMS-10 and DMS-100 couldn't hack that level of porting, so WE (Lucent) dropped the capability in deference to the less robust DMS switches.
[TELECOM Digest Editor's Note: Do you recall one difference between
> the way 'call forwarding' was originally set up and later on? People
> could 'chain call-forward', that is, you forward yours to me; I then
> forwarded mine to some other party; they forwarded theirs onward, etc.
> Let's call them parties 'A', 'B', 'C' and 'D'. People realized they
> could forward infinitly if they had enough co-conspirators to help
> them, and make a (considerable) long distance call for the price of
> a local call. The next generic of 'call forwarding' did not allow
> that. Yes, A could forward to B and B could forward to C, etc, but
> calls directed to A _stopped_ when they reached B. Calls directed to
> B _stopped_ when they reached C. Officially the theory was that
> persons calling A only wanted to talk to A. For A's convenience, his
> calls could be forwarded to B, but party A did not want to be
> forwarded onward to C or D. Or, so said telco. And originally, if A
> forwarded to B and contemporaneously B forwarded to A, it would start
> an endless loop until eventually all circuits in the CO were tied up.
> Telco quickly put a stop to that also. But that 'chain forwarding' was
> foolish anyway; people could rarely -- if ever -- make a series of
> short distance calls for less expense than a single long distance > call. PAT]