Which letter-cluster will replace the question mark (?) to complete the following series? PGD, SEE, VCF, ?, ?

ZBD, CYI YAD, BYH YAG, BYH YAH, BZH

YAG, BYH

PGD, SEE, VCF, ?, ? The logic followed here is : P → (+3) → S → (+3 ) →V → (+3) → B G → (-2) → E → (-2) → C → (- 2) → Y D  → (+1) → E  → (+1) → F → (+1) → H