One way to find out for certain would be to challenge them.
(obligatory - I AM NOT A LAWYER.. )
I *THINK* these things are supposed to be public record - so you should be able to request it from them. If they refuse to give documented proof you could always inform them (in a cordial and polite manner) that you will be releasing a product that includes KS 3.1 (I dunno - A Linux UAE complilation or something). I'm sure if they own the copyright they'll be more than happy under those circumstances to prove it
I am, however, 90% sure that when they bought the name, company, IP, that was all in there.
And what if it wasn't? You have to find out where the copyright reverts to... the original programmers? Whatever parts of the company that are left and owned by others.. So even if they don't own it (which is unlikely) you'll still have to find out who does.
I think it's good that someone out there is questioning these things - if you hit the lucky 10% and you're right - fantastic... if not, at least you tried..