Some information suggests 5-year began in 1979 to expire 12/31/1983 with the same format as standard trailers.
This information also suggests 5-year dates set 12/31/1983, 12/31/1988, 12/31/1993 and 3/31/1999, with the 1999 issue exclusively with "TL9" prefix.
1988: issued in 1983 with stacked T/R/L prefix which was standard in '83. Single year 1988 had full-size TL prefix.
First Issue 1980s?
"TP", "PT"/"PV" supposedly only supposed to be issued to motor carrier trailer (semi trailers, commercial). PT/PV mistakenly issued to private light trailers for years. "UP" (Utility Permanent) plates issued in the late 1980s and early 1990s, then DMV issued only PT/PV for many years. As of 2011, private light trailers only issued UP plates.
State Outline design, believed to be used only by Government entities?
"PT" prefix for Permanent Trailer
numbering began PT10001 to PT99999, then PT00001 to PT09999
then PV prefix, PV10001 to PV99999 (end circa Fall, 2014)
then 1001PT to 9999PT, then 10000PT to 99999PT
Redesign effective 5/1/2015