Evan I am not great with the exact way plants are named , I see a lot of contradictions at different sources. But as far as series go I think it is mostly for advertising similar to trade names. For example I know if a plant has Cone-fections It will be a double Echinacea from AB Cultivars.
And when strain is part of a cultivar name it seem to mean that they are not all true to form. Most times I try to avoid them because you never now exactly what you are getting.
Polly I would say that you are right that series could have strains in them.
