Schengen Visa: How to inform visa officer about the lack of a particular document?

So the situation is I work as a contractor for a US based company, hence instead of traditional salary slips, I have to raise invoices based on which my employer deposits money in my account.

I do have account statements, alongside copies of my invoices, from my employer that prove the money gets deposited in my account.

How do I convey this to the visa officer? Do I mention this in the cover letter, or do I need to mention it in a separate letter?

And a similar situation is with my tax returns, I have not yet filed for my tax returns. However, I have paid advance tax in the form of tax challan.