Mostly right John
The Reichswehr was having a problem with guns turning up missing, as a form of "gun control" and insurgents / commies getting guns, they implemented a requirement for marking the guns with 1920. Although this is the year it was implemented, it is not a true "date" although most collectors, including myself say "double date". You will see 1920 on later guns, but most are 1920 and 1921 time periods.
Ed