Drugs often cost a very specific amount of money (When I buy drugs it's always something like 4.86e or whatever, not neat 4.99) so I assume it's easy to de-anonymize
I'm not an expert on this, but I suspect merchants supporting level 3 data send it to the processor for all transactions, not just for corporate cards (if they even know it's a corporate card), but they only get the fee discount if it's a corporate card. Your credit card statement might not expose the data (or even get it), but the network can still sell it.
