Because some of them are sonically sealed and some are not.

See Archie's statement here for example.
http://slabfree.marlowcasinochips.com/whybeslabfree.htm

Note "The chip is then permanently sealed into a plastic case"

We believe that a number of the slabs weve seen with chips are not permanently sealed at all. In fact one of the companies at least is a guy sitting at home doing it all himself - grading, putting in the case, selling. I reckon I could open this type of case, change the chip and close it again without you knowing. If this is the case then you are in just as dangerous a position if you support slabs.

I dont know the answer until I see them in front of me. Neither do you or anyone else here.

Ive seen good scans of all the different companies 'capsules'. They all differ slightly. If they had been the same then I would not have bothered with them all. There is no point half completing the exercise now so I just bought them all in one go to get it over with.