Does anyone know what year the 20 & 30 round magazines were introduced for the Thompson SMG?

I ask because someone posted the following "goof" for "Public Enemies" on IMDB:http://www.imdb.com/title/tt1152836/goofs

He's insinuating that box magazines didn't exist until after the start of WW2..isn't this total BS? Weren't the 20 round magazines available when the the 1921 model Thompson came on the market? I'm not sure when the 30 round mags became available, but I thought it was prior to WW2. Can anyone clear this up for me? Thanks.