(We’re slipping away from the topic, but it’s been answered, so…)
I think this is a communication issue. I assume there simply aren’t enough output latches in a single ALU to hold a belt’s worth of outputs. Therefore either those results disappear before they would drop off the belt, or there’s a place they get sent to to wait for the belt to advance them away.
(This would likely require a pathological or artificial case to cause, but I think it deserves an answer.)
I would assume that such a place would be part of the Spiller system-its top layer, perhaps. And that an entry-based Scratchpad would be a logical extension of such a structure.