68 Trunk Weatherstripping

I have a dilema with the weatherstripping on my 68 Mustang Convertible. I'm about to finish 'redoing' the trunk compartment, and as part of the job, I wanted to change out the dried out and cracked weatherstripping. After shredding the old and prepping the trunk lid for the new, I found that my new replacement stripping has a big 'slot' in the middle of it. The original was a solid rubber piece. I checked a couple of other originals and they are the same solid piece. Both MustangsUnlimited and MustangPartsHouse have the same weatherstripping. So, I guess my question is, -what is the slot for and why is it not the same as the original? Anyone have any ideas? I'm stuck without a trunk till I figure this out. Thanks.