As part of my accounts spring cleaning exercise I am trying to get a pair of flights changed from my M&M account to my DC account (long story behind this. Basically LH made an error in crediting the flights to M&M in the first place). M&M are prepared to eliminate the record from my M&M account to enable me to apply for credit to DC. So far so good. Will DC credit the flights to my DC account without any fuss? I could easily envisage a problem because
(a) DC might be able to see that the flights had already been credited to M&M in the past (even though M&M have cancelled the credit since and they should now be open to be credited to any *A programme)
(b) one of the boarding passes has "M&M" printed on them. Will DC take this as "proof" that this flight has already been credited to a FF acount?

I just need to be careful here as M&M said they will release my flights but won't re-credit them in case DC turn down my retroactive credit request.

How big is the risk in your eyes, fellow flyertalkers? Given one-ways and miles&cash the miles would just go soooo much further in my DC account.^ But if this game doesn't work I will lose all those miles (20,000).

Thanks, ps