I noticed a similar but different issue when flying near Verdun in early 1917. Georges Madon from Esc 38 still uses a Nieuport 17 with Lewis in 1917 while the rest of the unit has switched to Nieuport 23. Madon has a unique N17 skin for 1916 but not for 1917. Since the squadron doesn't have a N17 skin for 1917 either, Madon actually switches to default N17 Lewis skins that has British roundels on it.

Flying in Jasta 7 I ran into Madon quite a few times and decided to fix the skin by copying the 1916 skin and naming it Off_nieuport17_Lewis_ace_t_Esc 38 1917_Georges Felix_Madon