No, AAxxxUS 001-999 were first, your DN5XXUS is identified as:
DN**** G-19 1.0 1988-03-01 First G-19s imported
DN***US G-19 1.0 1988-03-00 Austrian proof marks (although frame looks more like Gen 2). According to Glock it was the 346th G-19 imported into the USA. I\'m the second owner and bought it in 1990, its still all original.
A nice 2nd Gen G-19, I have BX/FA/FH/GS/TS prefixed G-19's.
So yours is 500th something of prefix DN.
GLOCKS #1 FAN!!!
"IN GLOCK WE TRUST"