Series 111 XJ6

OK, so not a Mk 10 or 420G but I'm currently looking at a 1983 XJ6 factory manual 5 speed, which are as rare as hens' teeth in Australia.
The problem is, the compliance plate indicates it is an automatic.
The seller, who appears to be very genuine, is about the third owner and has owned it since 1993 and swears it is factory original.
Could it be that the compliance plate is wrong?
Did these things happen back in the eighties?
I don't want to part with my hard-earned if it's not genuine but by all accounts it does appear to be the real thing.