Hi there, @smtwtfs.
Thanks for reaching out to us. Allow me to help and address your concern about check number, so let me get this straightened out.
Currently, QuickBooks will automatically assign a check number in the register and there isn't an option to disable it. For the meantime, you can manually change the check number when creating the transaction. 
For additional reference, you can check this article: How to edit check or paycheck numbers.
I can see how this feature would be helpful, you may want to submit this idea to our product developers so they'll be able to include this in their next product update.
Here's how you can send feedback:
- Click Help.
- Select Send Feedback Online.
- Click Product Suggestion.
- Fill in the feedback info.
- Click Send Feedback.
Please know that you're always welcome to post if you have any other concerns. QuickBooks Community will always here to help you.