I have just purchased my GSX1300R service manual, and according to Suzuki, the only difference in the fuel tanks, is with the California model which has a 20L tank instead of the normal 22L tank. I suspect this is to make space for the PAIR injection system which pumps airbox air into the exhaust to clean up emissions. Possibly, the specs you were reading were converted from gallons. We in Canada use the Imperial gallon, while the US uses their own gallon. (All this makes the metric system even more appealing) So if the tank capacities were converted from gallons to litres by an American and a Canadian, they would come up with different amounts. Or it is possible that somhow you ended up with the E-33 model which according to my manual, was destined for California. If you bought it in western Canada, this is possible because just like in the States, that is where our emissions regulations are the toughest.