To use a numerical example, assume you have 2 participants over the age of 50, both over the 401(a)(17) limit of $305,000 for 2022.
Part#1 defers $27,000 (the 402(g) limit + the catchup limit)
Part #2 defers $20,500 (just the 402(g) limit)
For 2022 they both have an ADP of 6.72% ($20,500 / $305,000 - since the catchup is ignored)
Now suppose that after running the ADP test it is determined that they each need a refund of $3,000 to pass the testing.
Part#1 has already used up all of his catchup limit and would receive a $3,000 (+/- earnings) refund.
Part#2 has not used any catchup. Since the $3,000 refund is less that the $6,500 limit, all $3,000 would be recharactherized as catchup and he would receive no refund.
The Plan does not rerun the ADP test after these corrections.