Unless, of course, when you want to retro-credit miles for flights that haven't posted. I'm sure they still want you to send in the original boarding pass (the PDF you received online won't do -- you have to "originally" print that) by snail mail, so that they can lose your documents and refuse credit.
HTB.
Hmm,..... never had any problem with retro-credit at M&M.
Only 1x it took 4 weeks for the retro-credit, usually miles are posted 7-10 days after I send snail mail to Verl.