Been wondering about this for some time; does anyone know what "Y2" signifies on ESA movement plates?
You can find this mark on ?all? ESA electrconic movements from the 1960s and 1970s i.e. ESA 9150 through to 9158 (the Dynotrons)...but also the ESA 9162 and 9164 tuning fork movements as found in Omega F300, Tissot Tissonic, Longines Ultronic, etc.
On the photo below, you can see the "Y2" on the far right of this ESA 9162 movement: