My Mustang is an original and the store I got it from said it was either a ’74 or a ’75. Nowhere on this guitar does it say when nor where it was made. I looked at the heel of the neck where it usually says the date, and all underneath the pickguard. Its Sunburst with a white pearloid pickguard. Anything additional, reply to me for (stuff on headstock ….pat. numbers etc.)
You could look at the serial number (in the decal or on the neckplate). The numbers on the back of the pots are also a good indication of the production year, usually these numbers consist of 7 digits: the first 3 indicate the manufacturer of the pot, the next 2 numbers indicate the year and the last 2 the week of production. E.g. 137 7850
means CTS, 50th week of 1978.
Lots of good info on http://www.provide.net/%7Ecfh/index.html