Sales fell 24%, down from 175,522 in 1998 to 133,637 units in 1999. In terms of product mix the base hardtop coupe was the lionshare of total sales at 73,180 units and 54.65% of total volume.
www.mustangspecs.com
And while the page nowadays is defunct, the WaybackMachine still has it:
https://web.archive.org/web/2008051...mpabay.rr.com/theflock/mustang/doorplate.html
The doortag may yield further information, but on the VIN: 1FAFP4048XF120285
1FA = Ford USA Passenger car
F = Active safety belts all positions, second generation airbags
P40 - Two-door coupe
4 = 3.8L, EFI, six cylinder
8 = VIN Check digit
X = 1999 modelyear
F = Dearborn MI
120285 = Production sequence number
So the 20285th Mustang produced in the 1999 run.
Considering there were 73180 units of this configuration totally produced, this one is probably from around April of 1999 (doortag should indicate the date more specifically).
Not sure if that answers your question tho...