How about installing both version on same pc? You created files with those plants in 7.5 infinte, then re-opened and rendered them in 9 complete?

Doesn't work, unfortunately.

What irks me most is this:
When I bought the Infinite version some time ago, I nearly decided to get the smaller version and buy the plant pack extra. If I had done that, I could have the plants unlocked for Complete 9.
Since I opted for the Infinite 7.5 after all, I spent more money AND have to spend another bunch of money to get the plants which I would have had without additional cost if I had opted for the less expensive solution.

Does this seem fair?