Checkis a regular verb so the past and past participle are both checked
You need year-to-date income and the past two years' tax returns.
No, "checked" is not a conjunction. It is a past tense verb that describes an action of inspecting something or verifying its accuracy.
Yes it is past tense.
The past participle tense of "check" is "checked."
Yes because checked is a past tense doing word.
Because that is the tax law for a calender year taxpayer for the filing and paying of any income tax that may be due for the past tax year.
The past tense of "check" is simply "checked."
The correct past participle of the word "check" is "checked."
Checked.
The word "checked" can function as either a verb (e.g., "I checked my email") or an adjective (e.g., "a checked bag").
You can file a another 13 after 2 years have passed from the previous 13 filing date.