How can i find out the PDA version installed inside a bricked or bootloop phone?

[Guest akiz0007]

i have a small mobile shop. sometimes i need to flash customers phone.
If a phone is bricked or, in bootloop, How can i find out the PDA version installed inside the phone?
I need to know that because i can re-flash the exact PDA file without any problem. Downgrade does not happen anymore on new devices. i need to know which firmware is correct for my device among hundreds of updates found on sammobile or other site. 
Thanks in advance