The emulsions sold commercially also warn you about reheating. It is in the labels and mentioned in the book "Silver Gelatin". In addition, they may add some stabilzers which are expensive and hard to get.

For example, Thymol (10% in iso-propyl alcohol) at about 1 drop per 100g of emulsion will prevent mold and fungus. I've mentioned addition of Tetra Aza Indene as a preservative. This is also discussed on Jim Brownings web site in his emulsion making portion of the paper.