I store all boarding passes in the iPhone wallet... going back since the airlines added that option...

I think the boarding pass is not required for a retro claim, it is good enough to provide the booking reference and say, sorry lost the boarding pass. They can look up you were on the flight.

Actually one time - with Sk - I had an issue that my flight did not credit and they told me via the retro claim team that I didn’t board the flight... even though I did send in the boarding pass.

Seems the agent messed up the boarding procedure and the FAs didn’t do their head count...

anyway, after pointing out that I took the return just 18 hours later and that there would be no way to get to HEL some other way they just credited the points without any comment.