"to ensure that the FSF would have standing to sue in the case of a GPL violation"
At least by the time of the acquisition of Cygnus, the copyright assignment for Cygwin was a conventional one which gave Cygnus ownership of essentially the entirety of copyright in the Cygwin library. If Cygnus earlier used copyright assignments that were effectively assignments to the FSF rather than to Cygnus, that is ... possible but strange.
There are two different things. Employees of the company of course assigned their work to us and then we made sure the appropriate entity (in practice mostly either us or the FSF) owned the entirety of the corpus. These assignments were third parties who contributed code, so we wouldn't have to chase down piecemeal assignments bit by bit.
Ah, I see. Cygnus employees were mainly contributing to GNU projects requiring copyright assignment where they weren't working on Cygnus-specific stuff, and were very often the maintainers of those projects (thus having responsibility to administer the FSF's copyright assignment policy), so I can see how the situation might have been thought of as 'you either assign copyright to Cygnus or to the FSF, whichever is appropriate'. And indeed there is some language maybe still on cygwin.com as of this date that says something a bit like that.
You're making things more complicated than they were. We had hundreds of developers; they weren't all the individual maintainers (though collectively of course we were, and de jure once I managed to split egcs off (now gcc) and get people comfortable with the idea of forking).
Everyone who worked for us just signed the usual assignment and we automatically assigned ownership (via the first blanket assignment) to the FSF where appropriate. No employee had to think about ownership -- if you worked on FSF code it belonged to the FSF.
And due to the way California law works, if you worked on FSF stuff on your own time but using a work computer (and we didn't care if you did) it'd automatically belong to us..which would automagically assign it straight to the FSF!
At least by the time of the acquisition of Cygnus, the copyright assignment for Cygwin was a conventional one which gave Cygnus ownership of essentially the entirety of copyright in the Cygwin library. If Cygnus earlier used copyright assignments that were effectively assignments to the FSF rather than to Cygnus, that is ... possible but strange.