If I had the Pro version of Poser 12 and then "sidegraded" to a newer version 13 that was a lite version, I would not expect any of my Pro files to load into the lite program.

But those plants aren't pro files per se. They don't need advanced functionality, they work perfectly well in the "smaller" versions. Just because they were part of a bundle now they're limited to that bundle - and there was never any hint at this limitation to be found anywhere.

Anyway, when an offer from E-on sounds too good to be true, it's never true.  Trust your instinct next time.  E-on is very ambiguous on its web site.

Sadly, this is true. Not the best way to get new customers and keep the existing ones.
If Carrara had a more logical UI I'd have ditched Vue long ago.