The Custom Server uploaded sensor values (Ecowitt protocol) are the same which are uploaded to ecowitt.net (i.e. all what is uploaded from your sensor "fleet" is what you see on the ecowitt.net interface - sensor values and battery status of the sensors you have).
It also depends on who does the upload - different consoles have their own sometimes limited set of sensors and sensor related data.
As for the GW1000/WH2650 console, there is a field map for the weather application software weewx which shows all available fields for sensor values (provided the respective sensor is active) of the GW1000 console known today.
https://github.com/gjr80/weewx-gw1000/wiki/Field-mapI speculate that the WN34S are the first set of eight sensors and the WN34L the second set of eight sensors of the 16 soil temperature sensors (S=soil, L=liquid).
Even though the weewx field map shows what the GW1000 provides when being polled, it should be the same content as what is pushed via the custom server functionality.
The sorting of this field map is weewx name ascending by character (while the sorting of the customer server string is different - see below).
Probably the HP2551 console sends the same amount data. GW1000/WH2650 and HP2551 cover the whole sensor portfolio of Ecowitt.
For my sensor "fleet" (see signature) the custom server posting of my GW1000 looks like below:
(s: string variable, #=field length => s:4 = string with field length 4; sequence is: field name, field content, definition is: field length, field value)
e.g. the field name station type is 11 characters long and the field content is "stationname"; its corresponding value is 14 characters long and the field content is "GW1000A_V1.6.6"
a:74:
{s:11:"stationtype";
s:14:"GW1000A_V1.6.6";
s:7:"dateutc";
s:19:"2021-05-01 22:03:14";
s:7:"tempinf";
s:4:"71.4";
s:10:"humidityin";
s:2:"39";
s:10:"baromrelin";
s:6:"29.940";
s:10:"baromabsin";
s:6:"28.907";
s:5:"tempf";
s:4:"49.5";
s:8:"humidity";
s:2:"51";
s:7:"winddir";
s:3:"180";
s:12:"windspeedmph";
s:4:"0.00";
s:11:"windgustmph";
s:4:"1.12";
s:12:"maxdailygust";
s:4:"1.12";
s:14:"solarradiation";
s:4:"0.00";
s:2:"uv";
s:1:"0";
s:10:"rainratein";
s:5:"0.000";
s:11:"eventrainin";
s:5:"0.000";
s:12:"hourlyrainin";
s:5:"0.000";
s:11:"dailyrainin";
s:5:"0.000";
s:12:"weeklyrainin";
s:5:"0.000";
s:13:"monthlyrainin";
s:5:"0.000";
s:12:"yearlyrainin";
s:6:"15.118";
s:11:"totalrainin";
s:6:"15.118";
s:6:"temp1f";
s:5:"49.28";
s:9:"humidity1";
s:2:"51";
s:6:"temp2f";
s:5:"50.90";
s:9:"humidity2";
s:2:"56";
s:6:"temp3f";
s:5:"49.10";
s:9:"humidity3";
s:2:"51";
s:6:"temp4f";
s:5:"50.00";
s:9:"humidity4";
s:2:"50";
s:6:"temp5f";
s:6:"-11.38";
s:6:"temp6f";
s:5:"50.18";
s:9:"humidity6";
s:2:"48";
s:6:"temp7f";
s:5:"43.88";
s:9:"humidity7";
s:2:"51";
s:13:"soilmoisture1";
s:2:"42";
s:13:"soilmoisture2";
s:2:"72";
s:13:"soilmoisture4";
s:2:"64";
s:13:"soilmoisture5";
s:2:"41";
s:8:"pm25_ch1";
s:4:"11.0";
s:16:"pm25_avg_24h_ch1";
s:4:"12.4";s:8:"pm25_ch2";
s:4:"15.0";
s:16:"pm25_avg_24h_ch2";
s:4:"13.2";
s:6:"tf_co2";
s:4:"70.7";
s:8:"humi_co2";
s:2:"41";
s:8:"pm25_co2";
s:3:"7.4";
s:12:"pm25_24h_co2";
s:3:"7.5";
s:8:"pm10_co2";
s:3:"7.9";
s:12:"pm10_24h_co2"
;s:3:"7.9";
s:3:"co2";
s:3:"939";
s:7:"co2_24h";
s:3:"863";
s:14:"lightning_time";
s:10:"1619689115";
s:13:"lightning_num";
s:1:"0";
s:9:"lightning";
s:2:"14";
s:8:"wh65batt";
s:1:"0";
s:8:"wh80batt";
s:4:"3.04";
s:8:"wh26batt";
s:1:"0";
s:5:"batt1";
s:1:"0";
s:5:"batt2";
s:1:"0";
s:5:"batt3";
s:1:"0";
s:5:"batt4";
s:1:"0";
s:5:"batt5";
s:1:"0";
s:5:"batt6";
s:1:"0";
s:5:"batt7";
s:1:"0";
s:9:"soilbatt1";
s:3:"1.6";
s:9:"soilbatt2";
s:3:"1.4";
s:9:"soilbatt4";
s:3:"1.6";
s:9:"soilbatt5";
s:3:"1.4";
s:9:"pm25batt1";
s:1:"5";
s:9:"pm25batt2";
s:1:"5";
s:8:"wh57batt";
s:1:"4";
s:8:"co2_batt";
s:1:"6";
s:4:"freq";
s:4:"868M";
s:5:"model";
s:10:"GW1000_Pro";}