The DLC Team was indeed working on these maps before we shipped Reach. The nature of development allows particular teams to roll off a project just as others are being thrust directly into the thick of the fight (Concept Artists aren't called upon to do a lot of testing, for example). DLC just went content complete last night at midnight. None of these maps ever had any potential to make launch.
http://www.neogaf.com/forum/showpost...postcount=9063
This is pretty much the same time frame in which the heroic map pack was release.