NHF – new heroes for Heroes V 3.1.

There is a 30% chance of a spell appearing. Moreover, there is a check for duplicates. That is, if the same spell appears, it is regenerated 10 times with a 100% probability. If it doesn't appear, then it won't appear.
So, in theory, the chance of it appearing is slightly less than 30%.

If that's the case, then my option still stands. Because the chance of a tenfold repetition of the existing spell is too small. Although I would add a safeguard of 100 or 1000 regenerations, depending on performance, just to minimize the absurd case where, after 6 misses, there is NO automatic success due to repetitions. Since such a situation is perceived as a bug (if the player knows about the automatic success after 6 misses), its chance should be minimized.