of course there is a difference. In the first situation, the hospital remains the creditor. The collection agency is merely a company hired to attempt to collect their money. In the latter, the hospital no longer has anything to do with the situation. The successor creditor is the entity that purchased the debt. So, do you have any idea which situation it is?

also, it appears there was more than one debt involved even though it was owed to the same entity., Could you explain that situation a bit more as well?