So the one in the PDF is yours?
Going by memory and the old eye-ometer, mines TB10557 and late 96 according to a record of serial numbers I saw online somewhere and the piston on mine has quite a bit more material wasted away further towards the back of the piston, and no welded on end where the crown is, plus it isn't stepped up in diameter like that one in the pictures which definitely doesn't look like it has a cylinder sleeve in it when looking at the picture of the cylinder slot with the piston head pulled back to where the cocking groove is, the stroke may be different as the pictured one looks to have the sear engagement further towards the piston crown whereas mine engages right at the very end of the piston.
The dummy piston or inner sliding spear assembly on mine isn't retained by circlip and doesn't have a central shrader valve or big o'ring around the back of it, instead being retained by a crosspin and a central grub screw to retain that, plus schrader port on the top edge of the spear assembly and the older soldered on scope mounts the rings screw to.Also the forward articulated cocking link on mine is two halves with spacers inbetween not solid like that one.
I've only ever taken the piston out of mine once not long after I got it as curiosity got the better of me, and I didn't separate the spear from the piston but I'm sure I don't remember a brass seal carrier being in mine, I've read from others that Theoben experimented quite a bit with different material seal carriers along with o'ring and seal arrangements, inertia weights with holes and without holes, what interests me most about the one in that PDF is the bigger diameter piston head, considering the sleeved down cylinder and wasted away piston was big enough deal to put in the advertising, I'm wondering maybe this one was an FAC version with a slightly longer stroke, no sleeved cylinder and a slightly heavier piston, I'm surprised if it is considering it looks like it has the 7.5" barrel and as far as I was aware the FAC version was only available with 10.5" barrel, I guess it could have been shortened after by someone if it was an FAC version, or alternatively maybe they were getting back some swept volume in the 12 ft lb models to improve the cycle in .177 caliber which I don't think was even available when I got mine.
Would love to know for sure, but that's my thoughts