The test is, what happens when you breed them together, and what happens when you breed the resulting offspring.

If you produce a Lesser/Mojave BEL, and breed it to a normal, you will get mojaves and lessers. You will not be confused as to which is which--the offspring will be, distinctively, either mojave or lesser, not some combination of the two. Thus, you know that mojave and lesser are two separate mutations on the same allele.

I'm not familiar with what happens if you breed a lesser/butter BEL to a normal, or what happens if you breed a black pastel/cinnamon super to a normal.

Pastel and lemon pastel, however ARE the same morph--they are not separate mutations. Lemon pastel is a line bred strain of pastel, selected for high yellow color with little blushing. If you breed a lemon pastel to a normal, what you get will not be as striking as the lemon pastel parent, and with continue outcrossing, what you produce won't be distinguishable from any other pastel. It will no longer be lemon pastel.