I agree with you it looks like an adult YLG for me, too. The other possible contender imo its an adult LBBG, but this should have darker wings with less contrast to black wing-tip in many and more black bajonnett on p6, always?)
Your pictures highlights a problem quite well. Shade and darkness value of mantle looks like a normal YLG looks like directly hit by warm (and coming from an flat angle) morning or evening light. This enhances darkness value and shifts it towards darker hues. This is most evident=serious problem in YLG and Common Gull (I havent found a reason, maybe others can?).
Yes, complete band on p5 is slightly narrower than an 100% YLG= its easy to find one with a broader one. But your YLG is easy within variation.
(And yes, Stuttgart is in the SW corner of Germany, where I (still) use a lazy approach when identifying YLG. Err, I promise to change this, as I know the experts read here too)