Hi Hankjam
Seems to vary a lot between brands Looking at the Tesco website some passata is higher then some tinned and vice versa.. seems to vary from 3.0 from Tesco everyday tinned toms to 6.4 for Tesco italian passata with basil.. Can't find anything in the teens though. Maybe the Tesco everyday is thinned down with water thus reducing the carb content.. I would guess the tinned toms you found might have added sugar hence their high level.
What does it say about added sugar on the ingredients?
Different stages of ripeness must make a huge difference, but I would be REALLY surprised if the manufacturers were required to test constantly through the season and adjust their labelling to match. Tomatoes have a quite short season anyway, so... Oh, I give up. this is making my brain hurt.
Best you can do is test and see which one suits you better.