Dt and most of the others don't exactly make an announcement whenever they get a new partner, which makes things a little difficult to keep track of. I don't know how it works if some of the partners are places where you also upload directly to, but I guess you could be taking earnings away from yourself. However, it's all or nothing with Dt's partners so most people would opt in and forget about it.

More info here. http://www.microstockgroup.com/general-stock-discussion/a-list-of-partner-programs/