Are you referring to purchasing 2018 Online Deluxe or the desktop CD/download version?
If your past online returns are in the SAME account as what you are using for 2018 Online Deluxe, then that does qualify for continued access to the prior returns. If the 2018 return and prior returns are in different accounts, it becomes more problematic in getting them unlocked, but we can tell you what to do.
Or if you buy 2018 desktop Deluxe (CD/download), that also qualifies for continued access to prior returns, but if they are locked, then TurboTax Support is required to unlock them.
Be aware that access to all online returns can ultimately expire if a paid edition is not used each year. See this FAQ on when access expires to Online returns:
https://ttlc.intuit.com/questions/3355524-when-does-access-to-my-prior-year-turbotax-online-returns-...
If you save your own copy of the return and/or the PDF each year (and even the tax data file, if desired), then you have control over it.
NOTE: Remember all printed copies, PDF tax documents, and tax data
files are very sensitive since they contain your personal ID
info, financial data, and possibly bank account numbers, etc. Be sure
to store them safely and securely to guard against computer theft,
hacking, etc.
