Hello Dave,
The OGC Interlock is not its own line per se. Green Ronin and PCI both have separate lines, which to this point have also had the OGC Interlock logo on them.
It was always the intent to Interlock those products that truly had a reason for interlocking, (i.e. products that compliment each other).
At the time that Bastards & Bloodlines was being produced, we didn't have any other product that could compliment it. Therefore, we did not.
The next product that will Interlock (albeit months apart) will be Green Ronin's Fang and Fury and PCI's Slaves of the Moon. The reason for their release being months apart is due to the extensive changes to the Lycanthrope rules in 3.5. Mike Mearls felt it might be best to hold off until after 3.5 was released so that the book wouldn't be obsolete within a few months of it hitting the stores.
Should you have any further questions, please let me know.
Best,