H1B COS not applied. Can it be used?

I am on H4, H4 EAD and recently switched to a new employer. I had a approved H1B with my old employer but never applied change of status so technically I am always on H4.

If I would like to be working on H1B with the new employer, Can i still make use of that H1 that i had with old employer where COS is never applied?

Its a 50-50 chance. You can apply for COS and see if USCIS approves it.

Sometimes, they claim that since you never used H1B, you were never counted in the cap.