How do the license tiers work?

Hello @skfabby and thank you very much for your response!

So just to clear things up:

Are the pricing tiers, linked to the typ of access you get to the assets?
Because looking at the CLA, it appears to be that way. Would that imply, that for most of the unreal assets, there would only be a professional tier, because most of them would require access source access?

Standard License under a Personal - Reference Only tier: you may access the Content as a reference asset only
Standard License under a Personal or Professional tier: you may access the Content as both a source asset and a reference asset

What happens to assets bought under the personal tier, after you reach 100k+ revenue?
So they are named license tiers, if you are making 100k+ are you still allowed to use assets you bought under the personal license? Do you have to upgrade the license?