What does "new" mean in scheduled discovery results?

I was examining the results of a scheduled discovery. Of course it discovered a 24 port switch that was already being monitored along with all 24 ports.

So, why did NPM find 24 "new" ports on that switch if each of those ports was already being monitored? I always see lots of resources that are not really new.

What constitutes "new" to NPM? For that matter, how is "Changed" defined?

Thanks.