Please, what's a lab loaner? And what's a prototype then and/or the difference between the two?
A Lab Loaner is most likely to be the complete/finished version of a game that was shared with outside companies for the purpose of review. Most would have been shared with magazines for the purpose of having written and published to hopefully coincide with the release of the game. They were to be returned to the company that produced the game, but I would venture a guess that most were not returned and then forgotten, by both parties.
A prototype would be an in-develop game. Could be anything from the very first functional version of the game all the way up to the completed version that would be ready for beta testing.