Being "abandonware" merely means that it is old stuff and
unlikely to cause trouble.
Even if it was released as "freeware" they are not giving up their copyrights.
I would not add "questionable" material to the soundpack. (If you just can't play without it, I suggest it should only be available as
separate from the
official soundpack.) SoundSense is a wonderful and amazing project. But being a non-commercial fan project is not much of a legal excuse.
Over 2 years ago I started to collect and edit sounds and music to add. Most of this was animal sounds. It's all still on my drives, either unfinished or never submitted.
I had also been working on a license.txt document that gives credits and usage permissions for the music and sounds - both for what is already in the SoundSense library and for what I was going to add. But I never finished it. And
one of the things that put it on hiatus was the few pieces left without permission. It threw me for a loop.
It seems redundant to ask for permission and give credit for 95% of the music and sounds and ignore it for the other 5%. If you're going
part way, why not save the effort and completely ignore stuff like licenses and CC conditions and use it anyway? Either that, or the project should be 100% legit.
That, and I feel like those who gave permission - either directly to me or via a creative commons license - would not approve of a project that's not entirely legitimate.
I had spent a
lot of time watching YouTube videos for sounds of Muskox, Bear, Bugs, Bats, Crocodiles, Alligators, Cub Leopards, Cub Panthers, etc. Then I sent the video owners personal messages asking for permission to use the animal sounds in SoundSense - a fan-made music and sound mod for a game none of them had heard of. And then, weeks or months later, I
might get a reply. Maybe 1 in 6 would reply - if that. Though, if they did reply they usually said yes.
Then there's the time I spent on
Freesound.org,
pdsounds and countless other places for animal sounds. (Quality animal sounds are
very hard to come by, especially for baby animals!) And the time on
ccMixter and similar for creative commons music that would fit a certain mood and might be dwarfy and medieval enough to work. And I
always saved the web link, license info, and any contact info.
Also, last time I checked the soundpacks, most of the content is either CC or public domain. The rest is largely original stuff recorded especially for SoundSense.
My point is that effort has already been made to stick with legitimate content. And with some effort it is possible to find
excellent quality music and sounds under either creative commons or public domain. Some of the stuff on ccMixter really is professional level. And it's
not hard to keep the web link and license info in a tiny text (notepad) file, using the same file name as the sound/music to keep it organized.