I'm probably wrong here, as I'm nowhere close to acheiving my APUG Chemical Guru status card, but TF-3's stated capacity may have more to do with the realities of fixation while Kodak's may have more to do with advertising. As well, TF-3's esimate may be the capacity for a single bath, while Kodak's is for a double bath? Anyways, TF-3's estimate is per litre and Kodak's is per US gallon, and there's 3.8 litres in a gallon so the numbers are pretty close. Who uses fixer until it's close to not working anymore anyways? To much at stake!
Murray