I have some initial results from sorting cards, and I plan to have more complete results next week.
Team Rocket Returns Koffing 61/109:
BAQ-X9N-3UU: 20 (66%)
BAQ-X9N-VTR: 5 (16%)
BAQ-X9N-631: 5 (16%)
Team Rocket Returns Hoppip 57/109:
2NW-GF7-40P: 11 (78%)
2NW-GF7-K3X: 2 (14%)
2NW-GF7-SQG: 1 (7%)
Emerald Electrike 47/106:
AM1-4LY-6QG: 23 (88%)
AM1-4LY-HTD: 2 (8%)
AM1-4LY-4PY: 1 (4%)
Ruby and Sapphire Torchic 73/109:
5ZA-HMN-GF6: 4
5ZA-HMN-GF6 (no e-reader)*: 15
5ZA-HMN-B0P: 1
The Torchic with the e-reader variant from the battle decks is interesting but is making it hard to interpret the results. None of these are statistically significant because I haven’t counted enough cards yet, but it does make me think there is a rarity factor to the serials.