2./NJG 2 was a Staffel, part of I./NJG 2 (the Roman figure for the Gruppe level)
In the Flugzeugbestand (
http://www.ww2.dk/oob/bestand/njagd/binjg2.html), "durch Feindeinw." is the sort form of "by enemy action" (air battle, strafing, AA fire, etc...), "ohne Feindeinw." is without enemy action (accidents)
As a general rule, NJG crews seem to form a team with few changes, but for each particular case you have to check (sickness, wound, retirement from active duty could happen).
To find when they flew, the only way will be to find the logbook of one of the crew.