I don't know... I agree that they are the same exact morph but as far as differences go there is usually a difference that can be seen with the adults, the babies not so much but you can see it as they mature. Plus if you look at a Butter Daddy compared to a Platty you can really notice a difference. This is just something I have noticed over the years. Same morph with slight differences, and yes I do think a Butter can look like a Lesser and a Lesser can look like a Butter until they get older. Here is a quote from RDR.
"The Butter is very similar in appearance to a "Lesser Platty"........BUT..........the Butters have more yellow coloration in their patterns. The yellow becomes stronger as they mature, where the Lesser's yellow becomes " less" as they mature."