Many mailers tend to look at their house file as one big suppression file when sending updates to the co-ops. In many cases, only a portion of the house file gets mailed in a typical drop, perhaps with the exception of the biggest seasonal mailings and depending on the offer.
One option is to leverage the remaining un-mailed names on the file by sending them to one or more of the co-ops for reactivation. Often times the timing of the merge processing and the co-mail schedules can tighten the window for using this tactic.
Instead, we suggest allowing the co-ops to bring into the modeling the names that are not being mailed for any given prospecting drop. Think about it: Using your older house records can help the models work better when they have access to all of those older responders to your offer. There are typically good records in the databases that will float back up to the top segments if they are still active mail order buyers.
Remember, those old records responded to your offer previously. It only makes sense to surgically target them for prospecting rather than leaving them off the table.