ITRF 1991 - ESRI:115732

WKT

VERTCS["ITRF_1991", 
	DATUM["D_ITRF_1991", 
		SPHEROID["GRS_1980", 6378137.0, 298.257222101]], 
	PARAMETER["Vertical_Shift", 0.0], 
	PARAMETER["Direction", 1.0], 
	UNIT["Meter", 1.0]]

WKT2

VERTCRS["ITRF_1991", 
	DYNAMIC[
		FRAMEEPOCH[1988.0], 
		MODEL["NNR-NUVEL1"]], 
	DATUM["D_ITRF_1991", 
		ELLIPSOID["GRS_1980", 6378137.0, 298.257222101]], 
	CS[vertical, 1], 
	AXIS["Ellipsoidal height (h)", up, 
		LENGTHUNIT["Meter", 1.0]], 
	ID["Esri", "115732"]]

Data from @esri/proj-codes

{
  "wkid": 115732,
  "latestWkid": 115732,
  "macro": "PE_VCS_ITRF_1991",
  "name": "ITRF_1991",
  "wkt": "VERTCS[\"ITRF_1991\",DATUM[\"D_ITRF_1991\",SPHEROID[\"GRS_1980\",6378137.0,298.257222101]],PARAMETER[\"Vertical_Shift\",0.0],PARAMETER[\"Direction\",1.0],UNIT[\"Meter\",1.0]]",
  "wkt2": "VERTCRS[\"ITRF_1991\",DYNAMIC[FRAMEEPOCH[1988.0],MODEL[\"NNR-NUVEL1\"]],DATUM[\"D_ITRF_1991\",ELLIPSOID[\"GRS_1980\",6378137.0,298.257222101]],CS[vertical,1],AXIS[\"Ellipsoidal height (h)\",up,LENGTHUNIT[\"Meter\",1.0]],ID[\"Esri\",\"115732\"]]",
  "description": "ITRF 1991",
  "authority": "Esri",
  "version": "10.4.0",
  "deprecated": "no",
  "areaname": "World",
  "extent": {
    "slat": -90,
    "nlat": 90,
    "llon": -180,
    "rlon": 180
  }
}