It is hard to say when the Charleston progressed into the Lindy Hop, but credit is often given to George "Shorty" Snowden for making the transition. The only known film record is his performance in the 1929 Film "After Seben" in which Shorty is performing some Charleston moves when he breaks open into a one-hand lead which gave rise to a new type of dance - Lindy Hop.
After Seben (1929) with Shorty George.(about 13 minutes into film)
Shorty George & Big Bea (1937).
Arthur Murray Shag training film (1937).
George "Shorty" Snowden (AKA: Shorty George) ... Listing in Who's Who in Swing Dance on the web.
Frankie Manning ... Listing in Who's Who in Swing Dance on the web.
After Seban (1929 Movie Dance Scenes)
Shorty George & Big Bea (1937)
Youtube (1941 Swingout Comparisons of Frankie Manning & Dean Collins)
Peter Loggins Histories (DanceHistory.org)
H. Leon Raper