Hello
Officially the I.NJG 4 and II./NJG 4 were established/founded in 1941 but never came to nightfighter operations. Operation Barbarossa demanded more Bf 110's for Zerstörer missions when the process to convert many Zerstörer units into the nightfighter force was at full speed. When I am right, Gebhard Aders 'History of German Nightfighting 1917-1945' has some more details about this confusing start of NJG 4.
The first real nightfighter Gruppe of the NJG 4 therefore was the III./NJG 4, founded in May 1942 from 1./NJG 1, 4./NJG 1 and 8./NJG 1. But soon after, the two 'missing' NJG 4 Gruppen were established again. By the end of 1942, NJG 4 had the I./NJG 4, II./NJG 4 and III./NJG 4.
Best wishes, Marcel Hogenhuis
www.fliegerhorst-venlo.net