When were HARN grids published by the US National Geodetic Survey?

Answer

"A High Accuracy Reference Network (HARN) is a statewide or regional upgrade in the accuracy of NAD 1983 coordinates using Global Positioning System (GPS) observations." (National Geodetic Survey: Frequently Asked Questions)

In connection to a HARN upgrade, sometimes called a re-adjustment, grid files are available that can be used to convert from the original NAD 1983 (1986) coordinate system to the HARN. The grid files were published by the US National Geodetic Survey (NGS) for different states, or groups of states, at various times.

The below list of principal datum tags should reflect the publication dates of the HARN grid files.

Note:
This information is copied from page 13 of the PDF document available in the Related Information section. The document, the Operator's Guide to the GEOCON software is from a beta webpage, so it is also attached. Be sure to check the NGS home page  for the latest information on GEOCON software.

If more than one tag is listed for a state, there was a later upgrade. HARN grid files were not published for later upgrades.

LIST OF PRINCIPAL DATUM TAGS
-----------------------------------------------------
AK Alaska         NAD 1983  (1992)
AL Alabama        NAD 1983  (1992)
AR Arkansas       NAD 1983  (1997)
AZ Arizona        NAD 1983  (1992)
CA California     NAD 1983  (1998)   NAD 1983  (1992)
CO Colorado       NAD 1983  (1992)
CT Connecticut    NAD 1983  (1996)
DC Dist. Columbia NAD 1983  (1993)   NAD 1983  (1991)
DE Delaware       NAD 1983  (1991)
FL Florida        NAD 1983  (1999)
GA Georgia        NAD 1983  (1994)
HI Hawaii         NAD 1983  (1992)
IA Iowa           NAD 1983  (1996)
ID Idaho          NAD 1983  (1999)
IL Illinois       NAD 1983  (1997)
IN Indiana        NAD 1983  (1997)
KS Kansas         NAD 1983  (1997)
KY Kentucky       NAD 1983  (1993)
LA Louisiana      NAD 1983  (1992)
MA Massachusetts  NAD 1983  (1996)
MD Maryland       NAD 1983  (1991)
ME Maine          NAD 1983  (1996)
MI Michigan       NAD 1983  (1994)
MN Minnesota      NAD 1983  (1996)
MO Missouri       NAD 1983  (1997)
MS Mississippi    NAD 1983  (1993)
MT Montana        NAD 1983  (1999)
NC North Carolina NAD 1983  (2001)
ND North Dakota   NAD 1983  (1996)
NE Nebraska       NAD 1983  (1995)
NH New Hampshire  NAD 1983  (1996)
NJ New Jersey     NAD 1983  (1996)
NM New Mexico     NAD 1983  (1992)
NV Nevada         NAD 1983  (1999)
NY New York       NAD 1983  (1996)
OH Ohio           NAD 1983  (1995)
OK Oklahoma       NAD 1983  (1993)
OR Oregon         NAD 1983  (1998)
PA Pennsylvania   NAD 1983  (1992)   NAD 1983  (1996)
PR Puerto Rico    NAD 1983  (2002)
RI Rhode Island   NAD 1983  (1996)
SC South Carolina NAD 1983  (2001)
SD South Dakota   NAD 1983  (1996)
TN Tennessee      NAD 1983  (1995)
TX Texas          NAD 1983  (1993)
UT Utah           NAD 1983  (1994)
VA Virginia       NAD 1983  (1993)
VI Virgin Islands NAD 1983  (2002)   NAD 1983  (1997)
VT Vermont        NAD 1983  (1996)
WA Washington     NAD 1983  (1998)
WI Wisconsin      NAD 1983  (1997)
WV West Virginia  NAD 1983  (1995)
WY Wyoming        NAD 1983  (1993)   NAD 1983  (1992)