PCGamesN has managed to get its mitts on some official Valve documentation. In it, the company tells developers:

"With Steam Bundles, if a customer already [owns] some items in the Bundle, they will pay for and receive only the items not already in their account. This allows the best fans of your series or franchise to 'complete the set' and get a deal on the remaining items in the Bundle."

We approve. Such a move should make it easier for PC players to take advantage of bundles and flesh out their libraries. For developers and publishers, however, it does mean some lost revenue that would have come from gamers paying full price for their bundles, despite owning a couple of the titles. Some, if not all of that money should be offset by a general increase in bundle purchases, however. If that's the case, everyone in the PC community should benefit from the new model.