These started on the 1977 base with number 1A*A1. It appears that they went up to 9E*Z9 (or something close) and then the series changed and restarted at A1*1A - but still on the 1977 (tan) base.
1977 BASE	1977 BASE	1977 BASE
1979 BASE Only samples were issued on the 79 base.
The tan base was issued up until 1992 - there were no blue plates issued except samples. The numbering on the tan base went as high as M9*9R. The 1992 graphic base started at N1*1A.
1992 SAMPLE	1992 REMAKE	1992 REMAKE David Doernberg - 1825
1992 David Doernberg - 1825	c.1997	c.1997
2003 Is this the first use of a "Q" on a standard-issue plate ? Kevin Halfpenny - 9069	2004 AVERY SAMPLE	2004 AVERY BASE
2005	2005 REMAKE Remake of 1978 base	2005
In 2008 Z9*9Z was reached, and the numbering continued where it was left off with the original 1977 base plates - this might be 1F*A1.