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

This is a known 'artifact' in PDP-11 history. DEC originally used the /10 designation for a cost-reduced 11/20. They never produced any, AFAIK - I'm pretty sure (without checking) that machine was re-labelled the /15, and those _do_ exist (I used one BITD). According to DEC documentation, the /15 has a KC11 processor, not the KA11 of the /20 (although I've never been able to find out much about the KC11 - I suspect it was a slightly modified KA11); the main functional difference listed is that it only supports one level of interrupt, not four; power-fail re-start is also optional, not standard. I have this bit set that both the /15 and /20 could be had with the 'simple' front console, that that wasn't the differentiator between them. The later /5-/10 pairing does indeed exist - I have one of each. They are absolutely identical except for the printing on the faceplate. Noel