You can get copies of your tax transcripts here.
https://www.irs.gov/individuals/get-transcript
You can get transcripts of your individual returns, and also your overall tax account. If the IRS disagreed with what you filed, you might see an adjustment in your transcript, but usually they would also send a letter. The IRS does not send letters when they agree with your tax return, they just take it. I suppose it's possible that they could cash your tax payment but lose the tax return in the mail and you would never know. You can verify what you filed by checking your transcript for that year.
