Problem comes in when shady collection practices START that 7 yr clock all over again everytime they "take over" the account to try and collect the debt. So in other words, Collection agency "A" may get it 2 yrs after you originally refused to pay.
But once the seven year limit is hit for the last time there was activity on the original account, you should be able to have all instances relating to that account removed no matter how many times the collection agencies have handed it off to each other.