The original Decca “Sunburst” or 3D label was used October 1934-December 1937.
Starting March 1936, the matrix numbers appeared to the left of the spindle hole.
From November 1936, labels list the phrase NOT LICENSED FOR RADIO BROADCAST in slightly larger fonts.
January 1938-July 1941: blue Decca block letter label with Decca in 2D letters and TRADE MARK REGISTERED above the manufacturing statement "Manufactured in U.S.A • By Decca Records, Inc."
De 941 - The chronological difference between these label variants is in the different label blanks. The first Decca label type has legends below the logo and along the lower rim in tiny print, and the description is in sans serif font. At first also the mx is absent, but from 689 on the mx is shown at 9 (698, 701 are exceptions). Last tiny print label known to me is 995 (exception 1035), and the next type with larger print is 998. I guess that for a short time a narrow font was used for credit and description (and thus occurs on some repressings, like here). Else there should be different printers.