How do you define "free bass accordion"? A unisonoric chromatic hand bellows instrument with single notes left and right? Kusserow bandionions were first built in 1903. A traditional C bass instrument with 2-row baritone basses (the low bass octave was only on Stradella; the "baritone" basses were taken exclusively from the chord reeds) was built by Venanzio Morino for Maurice Thöni, and Thöni went touring with it in 1919 (together with Antonio Piccoli).
For piano accordion players, Morino also constructed a two-row free bass in piano key arrangement (with the "white" keys in one row inward from the Stradella basses and the "black" keys in the innermost row with the expected gaps making for alternating groups of 3 and 2 "black" buttons, in "rotated" order like the piano players' left hands would be used to playing). Again we are talking about the 1920s here. As a series model, Hohner No 5555 had 41 piano keys in the right hand and 2 added free bass rows of buttons in the left hand (and could be ordered from 1932 on).
Attached are the specs of a 1934 Hohner-time free bass (on top of Stradella) instrument designed by Morino with a variable chord octave in the Stradella bass.
I have an accordion piece collection published in 1933 by Schott&Söhne that has several pieces suggesting the use of free bass ("Baritonbässe") in the left hand where available.
In the final Morino Artiste D series designed by Morino himself, the Artiste IX D and Artiste X D (with 5 and 6 Stradella row basses in addition to 3 free bass rows) were available from 1952, but you definitely could order these kinds of instruments earlier as well.
So I am not quite on the same page as you with regard to "totally new".