Well first we need to establish what you would accept as proof... what counts as not being forward compatible to you exactly? For example system libraries such as libpng or ffmpeg change versions and/or APIs between major distro releases, this inherently makes the old binaries no longer compatible by default. Is that such scenario acceptable to you as proof? Because I can list countless examples of those even just with one library being the issue, and there's so many more.
I'm not trying to trash Linux or act like I don't know what I'm talking about, I just disagree that most older programs work without any issues, especially GUI programs that rely on ever-changing system library versions, for the reasons I stated.