Reached my one-day limit of posts yesterday and couldn't re-post until now.
I think I hit the panic button a little too early yesterday....fearing you have to start all over after paying all the fees and completing most of the paperwork will do that.
Upon further investigation, I finally found the correct case # and invoice ID #. I was able to login to the ceac.state.gov site with the correct numbers. The case appears to still be active and all fees have been paid. However, the AOS needs to be completed by the petitioner and the IV applications need to be completed by the applicant. We're in Steps 4-6 of the IV process.
I still have some familiarity with the process, it's just been a long time since I dug into it but it's slowly coming back to me now. When I did this for my wife, it was all hard copies that had to be snail mailed. That forced me to double, triple and quadruple check everything before putting it in the mail. The online submission process seems to be less time consuming but also makes it easier to forget simple details (like the correct place to fine the case #) and having to get a new verification code every time you sign into USCIS is super annoying.
Thank you @Crazy Cat and @appleblossom for your expeditious responses yesterday!