[License-discuss] Retroactively specifying `-only` or `-or-later` for GPLv2 in an adopted project

[c.buhtz at posteo.jp]

Hello together,

My question in short: Is "GPLv2" by default "-only" or "-or-later" when 
the suffix is not explicit specified?

I am a member of an upstream maintainer team that took over a project 
[1] two years ago.
The project itself is round about 15 years old. We are the third 
generation of maintainers,
and we lack contact with the earlier developers.

The project is licensed under "GPLv2" without explicit specified suffix 
"-only" or "-or-later".
This is stated on Microsoft GitHub, in the license file, and in the 
header of each code file.
However, only the standard GPLv2 text has been copied without 
modification.
I have no further information about the licensing.

If I understand this standard text correctly, it does not clearly 
specify whether the
project is "GPLv2-only" or "GPLv2-or-later". To my knowledge there are 
no exclusive
license texts to this two variants. This distinction would need to be 
specified elsewhere.

How should one handle this if I cannot determine it with certainty, 
especially since I
cannot contact the previous authors? Are there any precedents for this?

Can I freely interpret the license and simply state that it is 
"-or-later"?
In this case the project would be more flexible to contributions in the 
future.

Are there any court rulings, guidelines, or recommendations from 
advocacy
groups (e.g., FSF, FSFE, OSSI, etc.) on this matter?

Thank you
Christian Buhtz

X-Posts on opensource.stackexchange.com [2] and in German on fsfe-de 
mailing list [3]

[1] -- <https://github.com/bit-team/backintime>
[2] -- <https://opensource.stackexchange.com/q/14980/27952>
[3] -- 
<https://lists.fsfe.org/hyperkitty/list/fsfe-de@lists.fsfe.org/message/JKDUOTHYYI6GLPED4AZTRPRSUJYDZFPH/>