There was plenty of discussion over whether or not the 584 would be included in any settlement, since trial was only about 148 and 336 patents.

We know now that it certainly appears that settlement was for the entire MMP.  Could the MOU pertain to this subject?  If ARM's tecnology is infringing, I doubt the Toshiba and Masushita want to sue ARM to get reimbursed.  Could TPL and those entities have agreed on what the 584 was worth and if monies are received from ARM in the future, they will be reimbursed, by lump sum or reduction of installment payments?  Could that be the "business relationship" that is referred to? 

But what about NECEA, you ask? I suggest they were not charged for the 584/ received a discount from the MMP cost, and hence no need for MOU. Remember NEC Corp was already a licensee.  Also NECEA readily agreed to the representative chip for chip families when that issue arose.  No doubt they got off easier than the other two entities and no MOU is not surprising.     All IMHO  Opty