Yeah, I understand the regalia is a "derecho adquirido" and as such everybody gets it, no matter what.
Even if they are serving jail time for robbing you with a gun they still get their Christmas pay.
Even if they only worked for one day, they are still legally entitled to a twelfth of whatever you paid them for that day.
If it only comes out to one or two pesos they may never come around asking for it, but thats a matter of convenience, not law.