TFS, Jan!
Whether we're making purchase online or in a brick & mortar, we sometimes need to remind ourselves to ask questions about the stuff we're seeing. Any online store that doesn't have a good 'contact' option is one to be careful with. And with B&Ms? If the sales staff isn't willing to do more than say "I don't know" or "this is what we have", I'd try to find another store & let the owner know why. Consumers have clout, but only if they use it wisely & (of course) politely.
Far as the 'guessing' on the alpha set, Jan? LOL BTDT myself, pal. Sometimes I got lucky, but other times I kicked myself for not shopping 'smarter'.
With stamps? Size (often) matters!