difficult.

i know one respectable and reputable breeder in germany appears to have lost track in parts of his collection, he had lots of BELs for sale that were labeled as "lesser + mystic/phantom/mocha/russo". basically guaranteed to have one copy of lesser, aaaand... well, some other BEL gene on top.

in your pairing, these two would be indistinguishable:
1/4 BEL (Lesser x Mystic)
1/4 BEL (Lesser x Mojave)
and both look extremely similar to super lesser. super mystic and mystic potion can also be hard to tell apart.

sometimes UV light / blacklight can reveal some pattern that is otherwise invisible, but i dont know if its useful here.

i guess the only way to be sure about the genetics (without proving them out) is to plan the pairings accordingly.

basically, pick and plan for pairings leading to unambiguous results. like mystic potion to super mojave, or super lesser to super mojave, or (if you can tell apart super mystic from mystic potion) mystic potion to mystic potion. or super mojave to lesser mojave, super mystic to lesser mojave, etc. generally super forms (or single-gene animals) make things easy and lessers/butters make things hard.

also if you combine lesser and butter, or mystic and phantom, you will never ever tell them apart again.