Resetting the year?

Hi.
Can anyone tell me how to reset the year in the dash? as my battery went flat in storage.
I have reset the clock, day and month but when I try to reset the year, it starts on 1981 go's up to 1997 then go's back to 1981. Is there something I'm not doing or doing wrong?
Thankful for any help.
Dave.

Won't go further than that i'm afraid, average life span of a car is 13 years so they have obviously allowed for that on the trip computer