Filename timestamp in Windows CMD batch script getting truncated

The first four lines of this code will give you reliable YY DD MM YYYY HH Min Sec variables in XP Pro and higher, using WMIC.

@echo off
for /f "tokens=2 delims==" %%a in ('wmic OS Get localdatetime /value') do set "dt=%%a"
set "YY=%dt:~2,2%" & set "YYYY=%dt:~0,4%" & set "MM=%dt:~4,2%" & set "DD=%dt:~6,2%"
set "HH=%dt:~8,2%" & set "Min=%dt:~10,2%" & set "Sec=%dt:~12,2%"

set "datestamp=%YYYY%%MM%%DD%" & set "timestamp=%HH%%Min%%Sec%"
set "fullstamp=%YYYY%-%MM%-%DD%_%HH%-%Min%-%Sec%"
echo datestamp: "%datestamp%"
echo timestamp: "%timestamp%"
echo fullstamp: "%fullstamp%"
pause

Output example:

datestamp: "20200828"
timestamp: "085513"
fullstamp: "2020-08-28_08-55-13"
Press any key to continue . . .