SERENA caught FLETCHLING, NOT ASH!
Accept Ash was the one commanding Fletchling in Battle against Viola.
That other Flectchling you saw might belong to Serena's Mother.
Trust me , I don't like Ash catching Flectchling more then you do.
I wanted Litleo for Ash because Litleo was more fitting more him.
Also , Litleo obviously will be more Marketable then a Flectchling .