?? 20500 mg = 20.5 g last time I checked.
Check again. 20500 mg of sodium is equivalent to 52.11g of salt. Here's the breakdown of my analysis based on generic (not brand specific) values:
5 tsp kosher salt (from dough and sauce) = 23.64g salt
2 # mozzarella = 17.08g salt
2 oz romano = 1.71g salt
14 oz pepperoni = 17.83g salt
total = 60.26g (I chose a slightly different precision than last time.)
As I said though, those are based on generic ingredients. I'm sure you could have some ingredients, such as your cheese or pepperoni, that include less sodium. Feel free to revise based on brand specific values.
EDIT: I just realized that you have 4 oz of scrap dough left over. That would eliminate at least a gram or two of salt.
EDIT2: I looked up the sodium content of Applegate Farms pepperoni and noticed it was marginally lower than what I used to calculate. So the salt (based on 490mg/oz sodium) would be 17.44g rather than 17.83g. In light of using 4 oz of dough less than the full 39 oz, and the brand specific pepperoni, I would estimate the sodium content is around 22789 mg, therefore the equivalent in salt would be 57.93g. This is a little closer to your number, and if I use the lowest amount of sodium I could find for a mozzarella cheese (116mg/oz), the total is instead 50.29g salt. So your sodium content calculation is well within reason for the quantity of ingredients you are using.