If I've already filed for 2019 but have previous years' w2s that haven't been filed (2017-2018) , am I still able to file those somehow?.

a 2017 W-2 can only be filed on a 2017 tax return

a 2018 W-2 can only be filed on a 2018 tax return.

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To do them, you'd have to buy the separate desktop/download software ....each year is separate...and install on you full MAC or Windows home computer....and Mail the resulting paperwork in at the post office...paper filing only for anything before 2019.

https://turbotax.intuit.com/personal-taxes/past-years-products/

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If you didn't file at all for those years, it would be a brand new file.

IF you did file either of those years, but didn't put in the W-2 forms...then   you'd have to AMEND your prior filings...and how to do that might get messy, depending on how you filed the originals.