Hello Petro,
02.09.2016 seems like a 1st cycle, juvenile Caspian Gull to me: quite broad pale edges to the tertials and a straight, leaf shaped dark center (against 1cy YLG) and quite uniform greater coverts with little pattern
05.05 2017 (2) looks like a 2cy Caspian Gull imo: quite a pale underwing with nearly unpatternend axillaries and a white stripe formed by the greater underwing coverts (a feature?)
05.05.2017 looks like a 3 cy Caspian Gull imo. But its hard for me to exclude other species here, Herring Gull (by really dark eye at this age?)
05.06.2017 is a bird, I would ID as an adult Yellow legged Gull in SW-Germany (dark red eye-ring and red gape), but isnt there too much white on p10 (underside)?
08.03.2020 is a 2nd cy Caspian Gull (?): diamond shaped dark centers to the pale mantle, uniform dark washed greater coverts and a (nearly) unpatterned white head
14.04.2019 (2): two adult Herring Gulls, with the rear bird maybe showing some Caspian Gull traits (slender, parralell bill and some dark peppering in the pale iris, at least I get this impression on my screen)
14.04.2019 (3) 2cy Caspian Gull by very pale underwing and pure, "adult-white" head and body (alone? at this age)
14.04.2019 a Caspian x Herring gull hybrid by general Caspian Gull impression (including a pale head and body, bill shape), but a very white, barred tertial and a (n appearantly) mixture of different shape of the dark centers to the upperparts and scapularrs (again: a real feature?)
15.12.2018: a 1cy Caspian Gull, but is the dark, much patterned underwing a sign of hybridisation with Herring Gull ? Its easy to see Caspian Gulls with a much whiter underwing in NE-Germany. Therefore variation or a feature of hybrids?
16.06.2018: a 2cy Caspian Gull (aged by worn bleached juvenile primaries and much pattern on the grey scapulars and upperpart feathers, not many pure grey "adult ones)
23.04.2017: a 3cy Caspian Gull by small dark eye and a pure white head (many immature looking herring Gulls have dirtier, more patterned heads (?))
And know I hope like you for Lou and others to confirm or correct. Thanks!