For SCI record book entry the two bottom tusks are used for the score. Lengths and maximum circumferences of the two have to add up to 15 to make the record book.
For Records of Exotics it takes 11 to be bronze, 16 for silver, and 21 inches for gold level. They use the lengths and bases.
I don't know what Trophy Game Records of the World uses right off, but they enter any animal as a trophy, then they classify them, based on the competition later. They put World record, world class, A, B, and C next to the entry in the book.