In an E-Mai, Bud Wachter wrote about the use of picks:
Until he died, Eddie Peabody used a standard shaped 1920s type tortoise shell guitar pick with some flexibility.
So did Harry Reser, although his were thicker, less flexible and a bit smaller. Harry filed and shaped his picks a lot -- perhaps to experiment or just for different needs.
Perry Bechtel used a thinner, small teardrop-shaped, tortoise shell with a rounded point up to the 1960s when he began experimenting with plastics. Finally, a friend at Emory University gave him some special material from which he cut his own picks. It looked like nylon and was thin and quite flexible.