Basic legal question: Publication of a fix to psgml

[Florian v. Savigny]

Dear listmates,

although this is a legal question, I am confident enough that most
people know the answer. It is this:

Some months ago, I fixed the "old-style backquotes" problem in psgml
(which was fairly straightforward, even if I did not even know what
backquotes are about), and I had inquired about this on this list
beforehand. Back then, Stefan Monnier suggested that we should track
down the other contributors to find out about copyright to see if the
fix can be put on ELPA. We have tried this, but many of them do not
seem to be available.

Now, my question is this: Given that Lennart released it under the GPL
(there is no separate LICENSE file, but all the .el files contain the
standard sentences to that effect), do I actually need any previous
contributors' permission to make the fix publicly available? (The
problem is not that I do not want to ask them, but rather that it has
turned out to be more time-consuming than I can afford.) Or,
alternatively, could I simply publish a patch?

The reason I am asking is that at least three other people have
expressed their interest in continuing to use psgml, two of them in
private emails to me. It seems a shame to me to let this (in my
opinion) great package go unused, and on the other hand, I do not want
to infringe on the rights of those who have written it.

Many thanks in advance,

Florian