I think the distinction is mainly that when they have them to sell, it will be distinctive in that it's the one they have to sell.
The ideal for me would be to turn back the clock and not sell my Rosco Bubbe mountain step through, code named Trusty MUSTy, and mistakenly referred to as the Medium Mountain Mixte. Medium Mountain Mixte caused extreme objections from those who correctly pointed out that the MMM was a step through but not a mixte at all.
I definitely want a true step through in my size, someday.
Bill Lindsay
El Cerrito, CA