I’ve heard from a few new users that are using the Faved By and Retweeted By screens to count how many favs they’ve received, or how many times they’ve been retweeted.
These pages don’t work for that purpose.
The Faved By and Retweeted By screens only consider your 100 most recent faved/retweeted tweets. This means the numbers shown on these pages will fluctuate.
Example: your 100th most recent tweet (from last week) got 100 favs. You tweet again and receive 1 fav, and your 100th tweet becomes number 101. Those 100 favs will disappear from the Faved By page, to be replaced with the 1 new one.
The pages are design simply to give you an idea of who is faving your tweets the most, and who is retweeting them - not to represent total favs and retweets.