there also has been some mixing and re-labeling and cross-labeling going on over the years.
if there is a difference, i say its as simple as this: lessers are more greyish/silvery, reduced in yellow and brown to a degree. And butters have richer yellows and browns.
i used to say its just one and the same, but now i know that some people work with both, lessers and butters, and picked the right lines, and in these collections you can actually tell them apart by color difference. even in combos like butterbee vs lesserbee.
anyway, they are still nearly identical, just pick what you like more. you will find lessers that look like butter and butters that look like lessers, as i say, lots of mixup and mislabeling over the years. just search for both until you find a BP or combo you like.