Are you referring to this thread?
http://ball-pythons.net/forums/showthread.php?t=93828
If so, I think you've gotten a little confused. Either that or I have.From what I understand, when the pairing was made, he thought it was lesser x normal. When an ivory showed up in the clutch, he looked closer at the "normal" female and decide it must be a YB, just one of the really subtle ones. And also, the male must be a YB lesser, or lesserbelly. I suppose it is also possible it is one of those extremely rare but possible things where the baby got 2 genes from mom.
There was also this thread:
http://ball-pythons.net/forums/showthread.php?t=93761
In that, people discussed the possibility of a snake that was both BEL and BlkEL, but that was all theoretical. No one knows for sure what that snake would look like.