There's also a good point in reframing the question to minimize survivorship bias, in order to best address the root issue.
During the 2011 Navy Yard shooting, an NCIS special agent had a SIG P239 with no spare mags. He ended up downloading mags borrowed from another LEO to reload his mag.
Yes, best practice would dictate carrying spare ammo, particularly if you're carrying a single stack gun. No, he didn't borrow compatible mags. However, it still gets at the root issue that it is an example where compatible mags would have been useful and relevant. We can't only look at examples where compatible mags were successfully employed, but that we should also be looking at incidents where they would have been relevant and useful.
Now, don't get me wrong. It's definitely a worst case sentinel event, and I'm not saying it's a super important issue. But, we need to ask the question/research the issue in an effective manner.