The five products, in the IRS's own names.
One of the five is not a transcript at all. The verification of non-filing letter is a letter, listed under "Transcript types" because that is where people look for it. It is the document a student aid office or a housing program asks for when someone had no filing obligation. Read its limit carefully, because it is the IRS's own: the letter "doesn't indicate whether you are required to file a return for that year." It says the IRS has no processed return, and nothing more.
Return transcript or account transcript is the decision that actually matters. A lender verifying income wants the return transcript, and the IRS says so: it "usually meets the needs of lending institutions offering mortgages." Someone chasing what happened after filing, an amended return, an examination adjustment, a penalty, a credit that was applied, a payment the agency says it never received, needs the account transcript, because the return transcript is frozen at the return as originally filed. Getting this backwards produces a document that is accurate and useless. The record of account transcript is the way to avoid choosing.
A wage and income transcript is a floor, not a ceiling. It is the natural tool for reconstructing a year whose paperwork is gone, and it comes with two limits the IRS states plainly. It "will only display information return documents that have been filed with the IRS which may not reflect all the information return documents issued to you", and it is "limited to approximately 85 income documents", above which it will not generate online at all. Information for the current processing year is generally available in the first week of February, so a January request returns an empty picture of a year that will fill in later. Treating this transcript as a complete income history is how a reconstructed return ends up understating income.
The reach depends on the channel as well as the product. Nine prior years of account and wage-and-income data are available through an Individual Online Account; the mail and phone routes return three. Older years than the online window go through Form 4506-T. Anyone who needs a decade of history should not start with the automated phone line.
These five cover individuals. A separate business transcript family exists and is reached from its own IRS page. A sole proprietor filing on Schedule C is still an individual filer for this purpose, but an entity return is not.