The data/iso-3166-2.json file is missing entries for AW, AX, BL, BV, CC, CS, CW, CX, EH, HM, MF, NC, NF, PF, SJ, and SX. I could be wrong, but it seems like this list is intended to include all codes from the standard.
See ISO Country Codes Collection or GeoNames or ISO 3166-1 alpha-2 - Wikipedia for details.