Ok Let's see if I can clear things up a bit.
- Regarding ADAC GTM 2013 and GTR3 classes.
They are two separate classes. Same car models sure, but with various different attributes where one is based on ADAC GT Masters in real life and the other is based on GT3 cars in general. They are not the same cars, but because they are similar and of same model they are what we call, overlapping content.
Those discounts Ricky78 mentioned are what we call linked discounts. As they're overlapping content (same model with different attributes in two different car classes) you automatically get 75% off for owning one of them in one class, which is about the cost of a livery. This type of discount is not a timed sale. It's forever.
The question about how this will work with sales (campaigns such as Christmas sales etc.) is still to be determined. Currently it hasn't been implemented that way. At the moment linked discount overrides any other discount but that's not necessarily because it's the intention, but because we haven't decided on how it should work yet.
Apart from linked discount, you also get discount for owning parts of a pack, which is dynamic and can differ from player to player based on what they own. If you had purchased one of the Radicals individually, the pack will get additional discount.
to me it seemed the same old price as the cars have always been, BTW, around 400 credits) otherwise this thing seems unfair pricewise.
This is false. We did have a cache refresh delay in the beginning which was fixed the next day after patch though. Maybe that's what you experienced. If you own Mercedes SLS in one of the classes the other one will be 75% off.
Basically, because I chose to purchase some cars ahead of time I am basically paying more for them than someone joining today. Even if I had the privilege to drive them for a longer time, that privilege wasn't much considering it was a hot lap game.
This is false as well. It's the complete opposite. You are paying less for having purchased and owning some of the content beforehand. I don't understand how you got to this conclusion. Just as an example we have Ricky78 on this thread who paid 1014 instead of the 1800 pack price (which is already discounted from the regular individual prices of the packaged content). He owned 2 cars in GTR3 class and owned DTM Experience 2013 which resulted in a 786 vrp deduction.
The whole dynamic discount system is made to reward people who are early supporters.