AmyMay
Situation normal
And of course EF, if your friend is local to you and the horse is also within a reasonable distance - you know who to get to vet it (A B).
I'm reluctant to write this as it sounds a bit narcy, but it is to help the current poster and future readers, so apologies if it upsets you.
Failure to resolve them on the first treatment is very common. Popping out more if the immune system is at all compromised, including by stress causing by simple things like leaving home, is very common, especially in a horse who already has multiples. My best vet says multiples are a different kettle of fish to singles.
I think the reasoning is that one is most likely one infected fly bite which had been contained, whereas multiples in different areas suggest that the virus is spread around the horse and may pop out anywhere.