If your e-file was rejected for having an incorrect 2016 AGI then that no longer matters.  You could have tried using zero for your 2016 AGI or you could have printed, signed and mailed your 2017 return if you were unable to e-file it.  E-filing for 2017 is now closed permanently, so 2017 returns must be mailed.  Did you mail your return?

Or did you have a different kind of PIN from the IRS that you are referring to?  Like a 5-digit PIN?  Or 6-digit PIN?

Is this what you mean?   <a rel="nofollow" target="_blank" href="https://ttlc.intuit.com/questions/3687911-what-s-an-ip-pin-do-i-need-one">https://ttlc.intuit.com/qu...>

Or this?  <a rel="nofollow" target="_blank" href="https://ttlc.intuit.com/questions/4047722-what-is-my-signature-id">https://ttlc.intuit.com/questions...>

are you saying that when I e-file my 2018 return all I'll need to do is put my 2017 AGI in at the end (since I have lost my 5 digit self select pin)

Correct in general.  However, if you filed late in the season, the AGI may not be in the database by the time you try to file your 2018 return in 2019 (yes, the IRS is slow, big surprise).  If you are rejected, you can try zero, and if that doesn't work you will have to mail your return next year too.  But if you file on time next year, they should accept your AGI in 2020.

you don't need the 5 digit PIN if you know the 2017 AGI **and** the IRS has put that info in their database, Sometimes that doesn't happen, then you have to file a paper return (in 2019)

each year you can select a different 5-digit PIN for the next time. Write it down if your e-File is successful, otherwise, Never Mind.

Every taxpayer needs a 5 digit e-file PIN.  You pick your own pin the first year you e-file and use it every year after.  If you don’t know it, you can use your AGI from the previous year.  The IRS has no procedure to generate a new self-selected PIN.  

Victims of identity theft may be assigned a second, 6 digit Identity protection PIN.  If you have an IP pin, you need both PINs to e-file.   The IRS will mail you a new IP PIN every year in December for the next season.  

@Opus 17 each year you can select a different 5-digit PIN for the next time. That is exactly what I do, and it has always worked.

You mean you can self-select a new PIN for next year assuming that your AGI works to verify you for that current year?

That's right.