Rulings
Q1: How does this Digimon's effect work when it has 3 digivolution cards?
Only multiples of 2 count for this effect, so even if you have 3 digivolution cards, it only gains Security Attack +1.
Data Sources
EN
Official English Card Listworld.digimoncard.com
Lv.6 WarGreymon ST1-11 SR Mega | Vaccine | Dragonkin [Your Turn] For every 2 digivolution cards this Digimon has, it gains <Security Attack +1>. (This Digimon checks 1 additional security card.)
A
Official English (Asia) Card Listen.digimoncard.com
Lv.6 WarGreymon ST1-11 SR Mega | Vaccine | Dragonkin [Your Turn] For every 2 digivolution cards this Digimon has, it gets <Security Attack +1> (This Digimon checks 1 extra security card.).
W
DCG Wikidigimoncardgame.fandom.com
Lv.6 WarGreymon ST1-11 SR Mega | Vaccine | Dragonkin [Your Turn] For every 2 digivolution cards this Digimon has, it gains <Security A. +1>.
JP
Official Japanese Card Listdigimoncard.com
Lv.6 ウォーグレイモン ST1-11 SR 究極体 | ワクチン種 | 竜人型 【自分のターン】このデジモンが持つ進化元2枚ごとに、このデジモンは≪セキュリティアタック+1≫（このデジモンがチェックするセキュリティの枚数+1）を得る。