As to suppliers-well, if they’re like me and grow them on themselves before selling, they know if the plants are hardy–but not necessarily if they’re labeled correctly (sometimes seed comes to me labeled as X and turns out to be Q, or some hybrid of X; if I’ve never seen or heard of X before and can’t find any references, X it is to me).

Large companies usually aren’t growing things on in a test garden the way smaller ones do, they simply don’t have the room–or the focus–to do so. They will be labeling as seeds/cuttings/divisions came to them, and so be labeled as correctly as they can. The only way you can be (more) sure is to err on the side of caution–more description, full Latin name, talk to the supplier if you can, etc.

With primulas, the best education you can get is to join a primula society &/or the North American Rock Garden Society, where you will be able to purchase seed by species. Of course…that seed will have been donated by other gardeners, with the uncertainty in labeling mistakes and bee hybridization that entails, but you’ll likely get wonderful things.

And it’s still a gamble. Some things that “should” be hardy for me aren’t, and some that “shouldn’t”, are. So his method of just growing a lot and seeing what stays, is perfectly valid.