PDP-11/20 vd one that just says pdp 11 what are the date differences?? OEM?

I have an original 1969 PDP 11 brochure. In it there are two PDP 11 model configurations to choose from; the 10 and the 20. For me at least this throws into question the whole "...the 10 first came out with the 5 in1972..." story everyone repeats over and over, unless one must have a "10" printed on the console in order to accept a computer model's existence. DEC must not have sold many original 10 models, and/or everyone who has a 10 does not realize that's what they have. But, facts are facts and the brochure and price guide I have is what it is. Hoping some here will check for themselves and consider it misleading at least to simply call the original PDP-11 a "pdp 11/20 without the nameplate". In short, the original bare-bones pdp11 was the pdp-11 10, the fully-equipped version was the pdp-11 20.