Rename all file in a folder with .BAT code

Question

thanks for your help in advice; I'm new on bat scripting and i need to write a program that rename all file in a folder keeping the file extension without renaming file already renamed.

@echo off
setlocal
set "folder=C:\StockSys\PcHost\IF\"

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%"

for /f "delims=" %%a in ('dir "%folder%" /b /a-d') do (
if /i not "%%a"=="%~nx0" (
set "extension=%%~xa"
setlocal enabledelayedexpansion
ren "%folder%%%a" "!fullstamp!!extension!"
endlocal
)
)


EXIT /B

This is what i'v written so far, it is kinda working, but if i'v got multiple files with the same extension it dosen't rename all off them, it renames only 1 x extension >> i provide a screenshot

i would also like to avoid renaming files already renamed but this script.

Thanks.