Does table 220.19 tell me that if I open up a range and it's stamped 12kw on the inside of door,I can treat it as an 8kw??

Yes- Absolutely- The text- first paragraph of 220.19. But you should look at the specs and see if they are specifying anything larger.

Which version of NEC are you referencing? NEC 2005 doesn't have an article 220.19, it skips from 220.18 to 220.40.

220.18(C) allows use of table 220.55 (range/oven demand factor table) for Ranges, is that what you're talking about?

I'm in the 2002.....Is that table just for your load calculation?