These newer belts with the pockets work just fine, as far as I can tell having just put a newer belt on an older pack. I recently purchased a 2012 hip belt to use on my pre-2012 Mariposa Plus at Gear Swap, but didn't notice the warning, in red, on the GG website that these newer belts will not fit on older packs. Good thing because I wouldn't have bought it if I had seen the warning. I would have assumed that belt would wouldn't work on older packs. The velcro is non-mating when combining a new belt with an older pack.
However, warning aside, the belt fits just fine and remains firmly in place without mating the velcro.
If you have been deterred from acquiring one of these new belts with pockets for an older model Mariposa, Gorilla, G4 etc., because of the disclaiming at Gossamer Gear, it slips through the loop on the pack and stays in place even though the velcro does not attach to anything. This can be remedied though by adapting either the pack or the belt so that the two mate and can be done easily without sewing or altering the pack. For me though, the belt remains firmly in place without adapting the velcro.