Im no matcher or anything, but heres what i think:
IB4200 are fragil, and require frequent atention. If you are only putting in around 3800 mha, you have bad cells.
You have to put youre hand on some fresh IB's. Buying loose, unmatched, cells from a matcher is non sense. At best you are getting old cells because they had were just sitting there for some time. Most probably you will getting the bad cells, that were matched but without the sticker. Not all cells are worthy of beeing 'team/world/race spec', and they have to sell them to somebody. Either as stick pack or as loose, "unmatched" cells.
I would get cells from somebody that DOES NOT match, preferably from HK, since is closer to the factory.
Sorry if im ofending someone, just my opinion