Yeh the 510 looks great but why did they slack off on the number plates?
My guess is it's because they got parts of it remodeled in time to make the cut, but didn't get around to the textures before then. Most of the "semi-premiums" are incomplete in this manner, one way or the other.
In many places texture seem to let cars down. I think a lot of models wouldn't look anywhere near as bad if textures were redone. The thing about that which annoys me is that fans could do it. I could even do it. Even if they're not premium quality, anyone could do a better job than the rot hanging off some of the standard models. GT is another thing that I wish was open source; or even just more modifiability. Minecraft for example is still successful as a paid game, but also incorporates a huge amount of malleability on the end-user's part.
The texturing isn't your usual single-canvas type affair, it's all very bitty and mapped using lots of transparency tricks, and on the Premium cars there are materials shaders to worry about, too.
Opening it up to the community would lead to demands to make the textures more like those editable from PC sims, but that just isn't compatible with the overall asset design paradigm PD has been using since the PS2. So half of the results will be terrible, and most people will complain about PD making life difficult, or about the lack of flexibility on which parts of the car are editable. Not worth it.
On the other hand, the bitty nature of the mapping means things like logos and number plates and headlights and so on might be more easily "fixed" in isolation. That's assuming the mapping holds up with the changes, because re-mapping effectively means editing the model, and that ain't gonna happen.
But, further, since these semi premiums appear to be works in progress, and any texture changes will be broken by model changes (unless the map is redone to be backwards compatible, which may obstruct any planned improvements in the texture coverage etc.), it just seems like a total waste of effort because none of that is circumventable without the community effectively being included in PD's internal communication, support etc. And PD may as well just hire people in that case; which they have done.