[ChrisMAg2]

Nick, I'm not quite sure if realy got, what you mean, but IMO the reason for your observation cannot be fixed on just one explanation. Actualy this can or might happen
•if parts of the reel was even just exposed differently from the rest
•if different batches of film are mounted together and then processed together
•if one of the reels underwent a differnt dev-process
•if something was changed on the entire copying process.
and/ or any combination of the upper mentioned.
It is almost impossible to specify, what actualy caused a change in color, unfortunaly! There are just too many posssibilities

@Etienne,
yes, those are real color photos. The reason for their effect is a partial fading/ desintigrating of parts of one or more color layer(s). This is very typical effect for (wartime) color material. This is not nessecarely due to age. Mostly it happened due to it's compostion and processing. Effects of age are a bit different. But that's a differnt story....