The Treasury regulations indicate a participant with multiple 403(b) accounts can aggregate them to determine the required minimum distribution (RMD) amount and then take the RMD from a single account (similar to IRAs). A person has worked for two different (unrelated) non-profit organizations and participated in a 403(b) plan at each organization (let's just say 403(b) plan X and 403(b) plan Y). This person wants to take the combined balance for Plan X and Plan Y to calculate the RMD and then distribute the total RMD from Plan X (nothing would be distributed from Plan Y).
Is it possible to aggregate across different plans like this or does the aggregation rule only apply to multiple accounts within the same plan?
Absolutely; that is the purpose of the rule.