I'm not sure anyone ever noticed this before.
The Yak9 T when you turn off tracers, the NS-37 still has a tracer in both AH2 and the alpha. With the IL2 the tracers on\off function works.
The NS-37 AP-T round had a tracer, there was no choice of not tracer. The HE round didn't have a tracer. Many sources have confused the rounds developed for the 37x252SR M1939 towed AA as 37x198 37mm NS-37 rounds. The M1939 had a large menu of round types being an AA gun.
The NS-37 had three rounds.
HE \ HEI with no tracer for either. Similar in shape to early M1939 HE-T shells (ogive body) but without tracer.
AP-T with tracer. Penetrated 50mm of armor at 200m.
Seems in the Yak9 T the bug is working backwards. The Yak9 T was only loaded with HE rounds. It could at least be reversed to no tracer with the single UBS 12.7mm using tracers to spot for the 37mm. And for the IL2, ahhh poetic license I guess for our kludge round system, unless the belt is all AP-T. Then there should be no tracer on\off for that NS-37 in the IL2.
The 23x152B 23mm VYa 23mm cannon in the IL2, the AP round did not have a tracer element. It had an incendiary under the nose cap that ignited during impact. Upon penetration into a compartment, you had a combination of tiny round and armor fragments and a high temp burning mist.
