The only error that is given by the validator is because I merged all of TC into one stop area. The validator should be updated to match since this reflects the on the ground reality better than the old tagging.

Regarding the stop area groups I would somewhat agree that this is a weird way of tagging them. I would however argue that it is the only practical way as the alternatives would be trying to agree on what should and shouldn't be included in one group. We avoid arguing about that by just mirroring what SL does. I also don't see an issue since the validator isn't giving an error. Warnings can be ignored if expected imo.

I took the time to compare them all below for a search between Uppsala and Stockholm C:
DB website (EVA?): from 7400102 to 7400002
Vy (SE) website (RHP): from 740000005 to 740000001
Trafikverket (PLC): from SE4351 to SE3751
Eurail (UIC): from 7404351 to 7403751

They are all different apart for ERA and UIC which seem to align for Sweden. Based on this I belive the RHP are not aligned with eva, at least not inside of Sweden.

The reason I moved the tag off of the station node is that rikshållplatser more accurately fits the stop_area since it refers to the stop (hållplats) rather than the station an example of this is Södertälje Syd where there is an upper level and a lower level station but only one stop.

What is the license for the DB api you'll use for your ref:eva work?

Some RHP values for german stations:
Berlin Friedrichstrasse: 800010125
Leverkusen Bf Mitte: 800051577
Wuppertal-Oberbarmen Bf: 800042951
Rostock Hbf: 800018830
Frankfurt(M)Flug: 800060379
Bielefeld Bf Brackwede: 800033048
Dresden Hbf: 800001305
Berlin Hbf: 800010100
Berlin Zoologischer Garten: 800010130
Stralsund: 800018510
Sassnitz Fährhafen: 800018521
Lübeck Hbf/ZOB: 800023565
Travemünde Hafen: 800023570
Puttgarden: 800023721
Berlin ZOB: 800034479
München Hbf: 800080600
Berlin Gesundbrunnen: 800010102
Hamburg Hbf: 800020400
Neumuenster: 800024643
Hamburg Bergedorf: 800020382
Hamburg-Harburg: 800020401
München Ost: 800080603
Hamburg-Altona: 800020403
Dresden-Neustadt: 800001301
Hamburg-Dammtor: 800020402
Schönefeld (bei Berlin): 800010120

I'm not so sure they certainly match the format but I don't really think that's enough. The reason for this could be that they're both used in hafas journey planners or that they both copied the UIC format. If my memory serves me correct however bahn.de does not use these ids but other ones which I presumed to be the eva ids.