The Delta phone app really is a nice tool. You can do so many things with it and conveniently pass through TSA and board your flight all with your electronic boarding pass. Old boarding passes are saved, for now, up to 7 days after your flight.
There can be an issue with this; what if you don’t get credit for your flight for some reason. Most times, all it takes is a quick email to Delta with the flight you were on that you did not get credit for and very quickly you are given credit.
The only problem that can occasionally happen is what if you don’t get credit. According to the 2014 Skymiles guide page 15 it says it is up to us to keep old boarding passes to be able to submit them, if needed, for full credit. If the digital boarding pass is gone you don’t have this proof anymore.
I have reached out to Delta about this and we will see if a change is made to have longer access but for now I would take the extra step to take a screen shot of your boarding pass or save them to a PDF or something like that. After all, every single RDM, MQM & MQD matters to us! – René