Wiktionary
y'all've
contraction (label en colloquial) (contraction of y'all have English)
Usage examples of "y'all've".
Gone to Sony or Panasonic or one of those guys and said (now reverting to a perfect American-yokel accent), We just love the VCRs that y'all've been sellin' us--why don't you make an electric chair that actually works?