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The only answer should be to follow the terms of the plan, not just to have a "paper trail."
I would agree that you should always follow the terms of the plan, but I also believe that it is prudent to have extensive documenation to show you are following the terms of the plan; thus requiring a "paper trail"
If the plan requires reallocating forfeitures, and you know a terminated participant (who I am assuming is 0% vested) was entitled to the forfeitures, I believe you should process the reallocation and then process a residual to forfeit the amount necessary. If you do not go through the steps of reallocating and forfeiting, it could appear (to someone just looking at the plan) that you missed eligible participants and did not perform the allocation correctly. Therefore, I would recommend having a "paper trail"