If you're not going to use the remaining transfers, you might be able to do a little test with them. Paint a piece of plastic card, apply the transfers and leave some for a day, some for a week and some for a month. At each interval, spray one of them with Dullcote and see what happens. You could even spray each set in pairs, one light and one heavy coat. It won't help your GUVs, but it might be of interest to other RMwebbers.
No pressure.