What does 'A' Grade Mean
Pretty much nothing. Certainly there is no industry recognised grading of this nature. There was a time when it was convention between manufacturers and distributors to refer to a specification in this way, but of course everyone had a different idea of what 'Grade A' actually meant. Nothing has changed, except lots of retailers declare their goods to be 'Grade A' as a marketing ploy implying a superior product, when there is no basis for that. The same applies for 'Prime'. The only way you can tell what you are getting is to look at the photographs you find on the retailers website, and then ask them what exactly is the grade of product.
The important thing to recognise is that these terms are now generally meaningless, so be careful what you expect.