Well my only suggestion is to sync in their data, use lookup to bring those 100 lookup fields.
Then have a very long if statement to point of errors
List("\n",
IF([field 1] <> [field 1 lookup],"Field 1"),
IF([address 1] <. [Address 1 lookup]),"Address 1"),
etc.
Then run a report where the warning message is not blank. The warning message will tell you which field needs to be updated in their system.
I assume your goal is to update their system, as otherwise you would be able to easily upload their data into your fields.