The issue Camelbaks and the poorly made copies all have 15mm clips as do the issue rocket packs, so this question has been on my mind as well.(i know i should get out more)But my opinion is that as they are made by the lowest bidder the company that makes them fcuked up with the size of the clips that is why there is so many for sale in surplus stores and on ebay.
The 'cheap' looking Camelbak copy is actually superior! I know it looks cack but the bladder has a better internal finish and is less likely to grow nasty stuff that'll give you D&V. Made in Israel by Source. Shame about the valve.
I did see a daysack thing that clipped on to that vest, clips were the right size and in all the right places. Came out from trials dept. label marked up with something to do with SF. Not smart I know but that's what it said. Really strange piece of kit with large drainage/venting eyelets all over it. No idea what it was for. No seperate yoke so it had to be worn on the vest. It wouldn't surprise me if the vest has been made with fittings as standard despite no one getting anywhere near the intended attachment.