I have literally seen those above mentioned movies, even after they were given to star. Dabang was telecasted on same week on two different networks. Which contradicts your above statement. May be after selling second output deal, after some months they got their exclusive tag for Salman's films.U r half right. Viacom18 had acquired rights of many movies right from launch in 2008 and continue doing so till now, what happened around 2012 or so was that they satellite rights of many movies expired and thereafter were taken by Star India or others. Ready, Dabangg etc were part of Salman-Star agreement.
After 2012 Viacom18 had sharing pact with Star India, they rent out few bollywood as well as dubbed south indian movies from Star India at certain ocassions. Also Viacom18 had a partnership with erstwhile UTV where they premiered home production films and 2nd output deal was handed to UTV. UTV on other hand gave 1st output deal of its home productions to Zee and kept later airing to itself. This is why u see certain movies on Zee+UTV and Viacom+UTV.
Well film or actor or studio agreements with channels is a complex thing. Sometimes all things need to looked closely to see the real picture or anticipate future happemings