User blog comment:Mich, Michele & Kuhla/Analysis: An In-depth look into Mechanics/@comment-7821941-20151212072227/@comment-3547897-20151213143523

If you have 2 conversion buffs on a squad, they will stack if and only if they're convering to a different stat.

Example:
 * Rec -> Def will stack with Def -> Atk but not with Atk -> Def
 * HP -> Atk will stack with Atk -> Def but not Def -> Atk

Also conversion buffs do not use other conversion buffs when being applied.