Illustrator :: Lost Changes To PDF After Save As Without AI Editability

I now have a PDF file that displays properly as a PDF, in Preview, Acrobat, etc., but when I open it up to edit it in Illustrator it shows me an older version. I'm trying to figure out if the AI elements of the file between that older version and the current version may be somehow retrievable, or if they're just totally gone.
 
Here's what I did, and what I've been able to do again (on two different computers) to replicate the same problem:
 
1. create a new file, and save as a PDF with Illustrator editing capabilities (let's call it test.pdf)
2. draw some stuff with the brush tool
3. save
4. save a copy, a PDF without Illustrator editing capabilities (testcopy.pdf)
5. draw more stuff with the brush tool
6. save
7. save as, a PDF without Illustrator editing capabilities (testcopy2.pdf)
 
Theoretically at this point, I should have one PDF that's editable in Illustrator (test.pdf) and one that's not editable in Illustrator (testcopy2.pdf) that look the same, and then an older version that's not editable in Illustrator (testcopy.pdf). (The uneditable PDFs were just to send to someone for review.)
 
Instead, test.pdf opens up in Illustrator to look like testcopy.pdf, not testcopy2.pdf. Any changes made between the 'save a copy' and the 'save as' (i.e. things drawn at step 5) are lost. Yet, when I open up test.pdf in Acrobat or Preview, it looks like testcopy2.pdf, the most up-to-date version. I'm able to open up testcopy2.pdf in Illustrator, so I haven't lost everything, but brush strokes have been converted to shapes, and what I need to do at this point is change the characteristics of the brush strokes.
 
I do recognize that I wouldn't have had this problem if I were working with an .ai file originally, which I try to do typically, but for some reason didn't here.