Do not feel terrified.

The reality is that the IRS is only going to ever look at FBARs if it believes that you have significantly under reported your income. In many ways IRS examinations are driven by a ROI metric. The IRS simply does not have the resources, nor the data matching capabilities for this to become an issue unless they are already interested in you.

If it would make you feel more comfortable you can simply file an amended a few of the earlier FBAR - I haven't checked the instructions, but I think all you need to amend is the original filing reference.

Alternatively you could just include in in FBARS moving forward.

Many would suggest simply doing nothing

 

Just start declaring it on the FBAR report if it helps you sleep at night. They do very little (to none) checking on what you report on your FBAR. If you really want to "come clean" you could also report the earnings from the Assurance Vie on your income tax forms. But you may want to consider simply declaring that as a "savings account" rather than as an investment account. The reporting requirements for a PFIC (which is what most tax advisors insist an Assurance Vie is) are seriously onerous. I know of people who have reported their assurance vie accounts like that for years and have never had any questions raised. (Given the state of the IRS these days, unless you are potentially avoiding a huge amount of income taxes, chances are it won't cause any problems.)