Each stat on each pokemon has its own IV, your usage of the word seems strange. I would use this link that a guy here had given before, https://pokemon.gameinfo.io/tools/iv-calculator (if you've recorded HP, CP, and stardust upgrade cost changes, you'll be able to limit down the possible IV's of your Snorlax to probably two at most combinations).
GamePress
Are you 100% positive about snorlax stats ?
I have made a few test with one of my snorlax.
To get the "right" CP I have to assume i have an IV of 9, but that gives me a max hp of 123 (while the actual one i had was 121).
The top is zubat's while the bottom is snorlax's.
