What specific dates should I enter on the TM7 form for my passport info?

You have to put the specific day on the right hand side in the line above...it's a bit confusing.

It is very clear passport expire date.

I have always put the issue date and valid until date of my original Non O visa based on marriage to a Thai which expired over 5 years ago in those boxes it says travel document number

The passport information is asked for to the upper right of that

If you are applying for an extension on a visa exempt I guess there is no document number

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I believe that the OP has the answer needed. Wishing success in obtaining the 30 Day extension of stay at your local Thai Immigration office for 1900 Thai baht. Be sure to have a TM30 on file with the Thai Immigration office.

That’s your passport information

Passport issue and expiration dates and place of issue

That is the DATE your passport was ISSUED and its EXPIRATION DATE.