In cattle there are two different breeds with double muscle alleles. One is missing the gene to inhibit muscle growth (deletion) and the other has an ineffective version of that same gene due to a transposed sequence (inversion?). It sounds to me like you are just explaining possible ways that the different leucistic het lines might be alleles - and I agree. However, I don't see how this explains the variation between lesser and platy within the lesser line.

All the cb platys have been produced by inbreeding within the line from the original platy. There have been lots of lessers produced by outbreeding but no platys have yet been produced without inbreeding. This is what makes me think the difference between lesser and platy requires being homozygous for a 2nd gene.