For 1971, the expiration month for the plate was stamped on the tag.
The 1972 tag introduced the "letter code" into the tag numbering scheme, in order to relieve tag number shortages in the more populous counties.
1973 introduced a simpler design to the state outline.
Even with the addition of the letter codes, there was still shortages of license plate numbers. Plates with the "Z" code were issued to fill the gap. The expiration month was indicated by a decal on the bottom of the plate. A car with a registration expiring in February would normally be issued a plate with a "A" code.