...
But yeah, the DR650SE has been unchanged since 1996. Wonderful bike.
Mostly.
Some tiny differences:
Some 1997 and 1998 models did not have the starter gear torque limiter. You want to have this item. Feel free to google "DR650 engine grenade" for explanation. It seems the affected bikes were retrofitted by the dealers under warranty (?) which means if yours wasn't dealer serviced it might still be as delivered

In 2004 the graphite compound cylinder base gasket was replaced with a layered sheet metal gasket. Besides making a top end overhaul some two hours quicker by cutting the time to scrape off the very persistent old base gasket it does not make much difference.
The reason for the upgrade is often cited as the old base gasket being failure prone.
I suspect the base gasket failures to be misdiagnosed timing chain tensioner gasket failures. Mrs. Le Cap's 2001 is still on its first base gasket after 109,000km.
Some slight differences between various country models:
Bread bin size taillight contraption on US / Cali models.
Rear carrier ("towel rail") on some bikes.
OEM alli sheet mini bash plate on some early models.
Headlight switch and park light on early German / continental European (?) model. These seem to have a different type / VIN starting SP46
Btoo. (?)
Besides that it's just a phletora of colour schemes (plastics white / tank white; then white / blue, yellow / yellow; black / silver; black / black; black & white / black and annually (?) changing sticker designs.
Short answer to the original question:
The year of manufacture and the stickers on the tank.