I have always thought this myself. I don't think I would ever buy a super form, white snake without looking at the sire and dam. Thinking about it, wouldn't you want to use a BEL that you knew came from two reduced pattern fires if you were going to pair it with an enchi? Conversely, if you were going to add to a busy patterned animal, then perhaps that wouldn't do at all.
That's why I am kind of surprised at the recent downturn in interest for male yellowbellies. While it's true that once you have an ivory you can add yellowbelly to anything, what are you adding? Males are still the least expensive way to introduce a gene. But I have seen awesome YB's, and average YB's, and some that you could bareley tell they were YB's unless you saw the belly. But even the latter can make an ivory. A good YB should be unmistakable from the view above, and the belly should only support that.
My daughter hatched two especially nice YB's this year from the same clutch. But depending on what was to be paired with them, there is no way a discriminating breeder would use both the same. If they were to sire ivories down the road, I would expect that difference could be crucial in any resulting pairings later on.