- RP bought brake duct designs from Merc as they were allowed to in 2019.
- They used those designs on the front of the car during 2019 and iterated them.
- They did not run the rear designs in 2019.
- They then picked up the 2019 designs and put them on the 2020 car (no iterations) BEFORE the rule change date, but AFTER the rule change was announced.
- Prior to testing for the 2020 season, Mercedes sent a set of rear brake ducts to RP after RP feared their own builds would not be ready in time.
- RP read brake ducts get built in time for testing, the Mercedes parts do not get used
- RP iterate the 2019 rear brake duct designs from Mercedes a small amount and start the season with them.
Looking at the rules, it's easy to see why RP did what they did. They are ambiguous and poorly written, especially to cover a transition period for a listed/non-listed part.
I think the FIA has tried to make everyone happy here. Renault because they get their protest upheld and RP are docked points that would be valuable against them in the WCC, and RP, because the fine was minimal, the points will hurt but they get to keep using the part.
I believe the reason for the FIA not banning the part and forcing RP to make new brake ducts is simple, and has been said multiple times already. How do they unlearn what they already know? It's impossible and they would likely design something that is almost identical.
Did they knowingly use the listed part design for 2020? Yes. Did the rules state they couldn't because they purchased the designs legally the year prior? No.
The only people we should be annoyed with is the FIA for writing, once again, poorly worded rules. F1 teams working in grey areas is a tale as old as time, and RP have done it here.
Why the fuss from the other teams? Well from the first days of testing they could see RP was quick, and was a threat to their WCC hopes, and in turn, WCC prize money. Renault are the only ones that had something they could actually protest, all the other teams could only moan publicly about it. Now the protest has been upheld, and all those teams wanted a harsher punishment they have something they can suddenly get in on, so they are damn well going to do it because beating them in a court room is cheaper than beating them on track.