I'm not 100% sure of the situation but it is possible to have $6K of catchups here. If you allocate $38.5K as PS, then you have total allocations of $61K and can determine that $6K of deferrals were catchup and $16.5K regular. In other words the 415 limit is in fact $61K. I like to say that we determine catchups (after some limit is reached), not the participant or the payroll company.
Likewise a participant cannot defer $6K and say it is all catchup (e.g. to improve ADP testing results). If no limit is exceeded, it's not a catchup.