Also, you might be forgetting that the distances of the stars that exploded will cause us to see them at different times. Say three stars exploded in a given year but one was 1000 light years away another was 1500 light years away and the third was 2000 light years away. We wouldn't see those novas here on earth in the same year. So, while it's quite possible that there are 2 to 3 novas a year, we may (i.e. likely will) see them many years apart.

On the flip side, a star that exploded 100 years ago that was 100 light years away and another star that exploded 500 years ago and was 500 light years away would appear to us in the same year here on earth.

Also, you might be forgetting that the distances of the stars that exploded will cause us to see them at different times. Say three stars exploded in a given year but one was 1,000 light years away another was 1,500 light years away and the third was 2,000 light years away. We wouldn't see those novae here on Earth in the same year. So, while it's quite possible that there are 2 to 3 novae a year, we may (i.e. likely will) see them many years apart.

On the flip side, a star that exploded 100 years ago that was 100 light years away and another star that exploded 500 years ago and was 500 light years away would appear to us in the same year here on Earth.