Serial number 1D0309820...
"1D" (the first parts of the serial number) means that the vacuums was made in the 4th quarter of 2001. If it were "5B," it would mean that it was made in the second quarter of 2005. The numbers afterward are the number of the model off the assembly line, which makes it number 309,820. That's a nice vacuum!
I like Riccar/Simplicity vacuums. I worked on them for years, and find them very user friendly, and for the most part well designed. When Riccar's tandem air vacuums first came out, they had issues, but Riccar noted and corrected them. One thing I love about the company is they are quick to update and fix any quirks their vacs have. Other companies just ignore the problems, or take years and years to address obvious flaws.
I find the tandem air vacs very easy to work on, but there's lots of screws (at least they're all the same size!). The dirt path is very short, and goes straight to the bag. There's a dial that diverts the suction to the hose for tool use, so all the dirt isn't going through a mile of tubing before it reaches the damn good HEPA bag (they redesigned the HEPA bags and they're probably the nicest vacuum bags I've ever seen).
I would say they're one of the world's finest vacuum companies today!