I heard back from tech support at Van's. Someone reported a change in stall speed/handling without the gap seals. Van's performed test flights and confirmed there was a difference in flight characteristics without the seal prompting the revision.
I have been flying two RV12's recently. One with the gap seal installed, the other, awaiting paint, without the gap seal. I noted the flare/stall characteristics of the plane without the seal were more abrupt. Most notably, when I expanded the wing skin fuselage gap to 3/16 inch in preparation for seal installation and paint, the flare/stall characteristics became even more abrupt. I needed to add power on virtually all landings.