From: San Antonio, TX
A pre and post-nuke screenie of Nagoya's city screen (with production) would be most welcome, Miller.
Sorry, a bit to technical for me. However I ran the turn before the attack again and noted down the pre bomb industry levels. Looks like I permanently lost 80 LI and 50 HI, nothing else lost, only damaged slightly.
OK. So, according the manual, p. 264, section 17.0 "Victory Points", it's 2 VP per unit damaged, 20 VP per unit destroyed. HI/LI, etc. can only be destroyed by firestorms or A-bombs, but is worth 10x the value of merely damaged factories. A previously damaged factory can be destroyed and yield another 18 VPs.
For your Nagoya, Miller: 20 VP x 80 (LI destroyed)+ 50 (HI destroyed)= 20x130=2600 VPs.
2600 VPs from the identified destroyed factories, but there's still a sizeable body of unidentified VPs. My guess is the balance came from other resource, naval shipyard, aircraft factories, etc. Without seeing more detail pre and post-bomb, I can't help you identify where those VPs originated further, but this gets you half way there.