Well, it seems as if the uppers are different depending on what frame you've got. I think you wanted this one:
Sig Sauer P229 9mm Caliber Exchange Kit 15rd
It's compatible with:
P229 with Exeter, NH frame chambered in 9mm (that came with a 15rd magazine from the factory)
P229 with Exeter, NH frame chambered in .40 S&W or .357 Sig
P229 Classic chambered in .22 LR
P229 with German frame chambered in 9mm
This kit will not work on:
P229 with German frame chambered in .40 S&W or .357 Sig
P229 with German frame chambered in 9mm with 13rd magazines
P229 with Exeter, NH frame chambered in 9mm with 13rd magazines
But I think you got this one:
Sig Sauer P229 9mm Elite Legacy Caliber Exchange Kit
Sig Sauer P229 9mm Elite Legacy Caliber Exchange Kit.
This kit is for 229s with German frames and is not compatible with Exeter, NH frames.