OK, this is probably one of the stupidest questions asked on here:

I saw a Discovery listed as a "Disco I" but made in 1998. As far as I knew, the Discovery II was launched in 1998.

Was there any overlap (ie. did they make and sell both in 1998)?

 

D2's were first sold as a 99, All 98 D1's that did not sell in 98 were retagged as 99's and sold till Rover was out of inventory.