1979 Submariner ref 1680 Re-Lumed

[Gaff65]

I've recently inherited my Dad's Submariner ref. 1680 and as the patina on the hands is missing on the dial markers, I assume it was re-lumed at some point. My question is this...When a dial is re-lumed, is the original Tritium removed or just painted over? If painted over, is there any way to remove the second coat to restore it to the original Tritium? Thanks in advance to whomever cares to chime in.