I was seeing it in the inventory page. I have since fixed the problem by restoring to an earlier inventory and doing some corrections. I'm still not quite sure how I ever got fewer results than distinct cards (I might have written the numbers down incorrectly).
I'm 99% sure it happened like this.
1. Entered a bunch of cards into the inventory.
2. Created a .csv file to upload, including some additional copies of cards already in the inventory, but forgetting to fill out the Condition & Language columns.
3. Upload.
4. Export entire collection. Now the copies uploaded without Condition/Language information are separate rows.
5. Auto-Fill the Condition & Language columns (now the copies of some cards are split across multiple rows, e.g. 5 copies of NM English RTR Abrupt Decay are split into a row of 4 copies and a row of 1 copy)
6. Remove collection and replace from the "corrected" .csv file.
7. Now you have two entries for NM English RTR Abrupt Decay, one with 1 copy, one with 4.
The better way to fix this (in hindsight) is as follows (this is as much to fix this in my mind for the future as it is for anyone else who ever has this problem):
At Step 4, use excel filtering to cut out the rows missing the information.
5a. Reupload to return the inventory to the Step 1 state.
6a. Fix the Step 2 csv file by putting in the Condition/Language.
7a. Upload a corrected file, and DeckBox will combine them properly.