Hi Franck,
just a slight correction to your assumption
'5/4' means 5th April to the French and most of the english-speaking word, including NZ
'5/4' means 4th May to Americans.
The NJG11 strength return for 5th April ("5/4") includes the WN of aircraft on- and off-strength, and thus the WN of recent losses of aircraft are often shown. In this case, the WN of two Bf109s lost on the night 3-4 April are given in the strength return, while the actual losses are also individually reported in seperate ULTRA decypts.
Cheers
Rod