sorry ,but alf did play chords too,
as someone who can speak with some authority on english concertina song accompaniment, visit dick miles you tubemusic and you will hear a lot of english concertina song accompaniment., plus I have wriiten a tutor with 20 examples of my accompaniments.
in my formative years i heard a lot of alf edwards and bert lloyd.
alfs song accompaniment was certainly a lot simpler than mine, but he certainly used chords, not just single line melodies.
it is my opinion, that Peggy Seeger is a talented all round instrumentalist, who had some lessons from alf but developed her own style, much of that style was developed by herself and through her instrumental talents with other instruments.
louisa killen[ I am fairly sure if my memory serves me right had lessons from alf], but does not to my ears sound like alf either