I would suggest fertilizing heavy during the growing period, works best for mine.. spring through summer. I use osmocote with alternating Jacks 20 20 20 diluted 10-1. Dosnt seem to do much in winter, and I am in zone 10b so my season is basically year round....I bought it from Wigert's in summer of 2023.
I usually use Alaska fish emulsion during the winter. I am not going to fertilize it just to see if the variegation stays around. Water around this area does have some calcium but not much Chlorine. Have only sprayed with water occasionally.
I got a reply back from Wigert's. Apparently they have a few that are doing the same thing. Erik said it is because they are to wet. So I guess I will watch it and see what happens.Isolate it and treat it with extra care. BRT don't seem to have pest problems so no need to spray. Fertilize regularly and wait and see. It does not look like a deficiency to me and it looks healthy with no brown leaves. I think you have the real thing.