Recently I hit an extra digit when setting up a custom new card session and was stuck with hundreds of new cards to review. Desparate to fix this, I started poking around the Anki collection SQLite database, I found the collection data responsible for the extra cards. In the col table, find the newToday key and you’ll find the extra card count expressed as a negative integer. Just change that to zero and you’ll be good.

Later I discovered another blogger found it too!