Can exclusives upload their new pictures to TS, because I read somewhere that only 18+ months old exclusive images can go to TS?
They can, but if they do the pictures go only to the Partner Program - for the first 18 months, they can only be on either iStock or the PP, not both at the same time, although they can be moved from one to the other on request (except that doesn't seem to be working very well just at the moment).
I don't see why anyone would upload new images to the PP myself but I suppose iStock felt they should give us the option.