The initial IRS checking of your tax return is done by the IRS Automated Underreporter system. This system checks you tax return against the information returns filed by the various payers of your income but does not seem to look outside this information to thing such as previously filed tax returns. Catching a discrepancy with regard to basis reported on a Form 8606 would likely come later, if at all.
IRS tax-return processing status show the IRS currently processing amendments that were filed in January 2026, three months behind. I imagine that the influx of amendments between January and today means that it could easily take six months to process your amendments, so it's possible that the automatic extension could expire before you r amendments have been processed.
https://www.irs.gov/help/processing-status-for-tax-forms
With regard to Forms 8606, the IRS instructions say for you to keep your filed Forms 8606 forever. This suggests that if the IRS has any question about your basis, the IRS is going to want you to provide copies of those saved forms and any other documentation that you have to support your basis. My feeling is that the IRS does not research your old filings to find information to support your position but instead places that responsibility on you.
Of course it doesn't hurt to request a filing extension and file later, but if your tax return shows a refund, filing later would delay your refund. If your tax return shows a balance due, that still must be paid by April 15.
