Forza Horizon 2 Promo Pictures

I finally got 340/340 of the promo pictures but the total to be taken did not go up and per the Horizon Promo Progress there were still 11 uncollected. I decided to purchase one of the cars and took its picture. The total count then went up to 360 but there is only a total of 351 to collect. Will 9 more cars be added, will there be an update to decrease it to 351 or is this it for FH2 since FH3 is available?

Update: The photo counter (progress after taking a picture) stays at 340/340 but the submenu of Horizon Promo Progress the total taken goes up as you take more pictures.

The promo reward counter locks in at what you said: 340/340. However I do believe you continue to receive the 1,000 credits for every car past that. And Horizon 3 has been out for going on almost a year now and Forza 7 is soon to come. No updates for Horizon 2 should be expected.