I've consulted with 5-6 accountants and people who've had the issue before. The advice I received boils down to:
"If you do not attach your 83b with your personal tax return it is not effective. However you can still correct the requirement to file it along with your tax return, because you are within the 3 year window of when the return was originally due."
So you can amend your return/file it late within a certain window and things should be OK. The accountants that have confirmed this are Vanessa Kruze, Wray Rives and Augie Rakow - all of them corporate and credible accountants. You also need to keep onto the confirmation the IRS sent you in case of an audit.
There is nothing on IRS.gov about attaching your 83b on a filed late or amended return but those accountants are people who say they've seen it happen frequently, have consulted with the IRS for solutions and that's the one they'd advise one to do in such situation.
disclaimer: I am not a CPA