It doesn't make any sense. Tax return for 2023 ia independent from tax returns from previous years. I would've included everything I had / could get and brought 2023 tax return to the interview. It's not the end of the world, but could result in unnecessary RFE and delay.
You're right, employment history is asked in part 8.
I just still don't understand how anybody can file N-400 and the very next day remember something is missing. To me it just means, it was filed in a rush without preparation.
You can prepare an errata sheet (ask lawyer about it) and update your application at N-400 interview. This, along with missing tax returns is decreasing the chance of instant approval and same day oath.