Well, I am just clarifying, initially you stated that MR receivers didn't have droop issues, as you can see that is not the case, MR receivers did have droop issues, if I'm not mistaken, I believe that all MR receivers were made in Ilion NY, there were some Marlin made barrels that had North Haven roll marks that were sent to Ilion but all the Marlin made receivers that were sent already had the 91 serial numbers on them, hence the reason you have 2009 and 2010 manufactured rifles with 91 serial numbers.
Remington was allowed to use the North Haven roll mark on Remington made barrels for quite some time after the move to Ilion, so that would explain why some rifles have the North Haven roll marked barrel and MR receivers, if your North Haven roll marked Barrel has the REP proof mark, it was assembled in Ilion, and is possibly made with 100% Remington parts, just an FYI.