@Wallaby given your situation of
(a) having filed I-407 correctly and intime and missing to file form 8854 and because so many years have passed, I would file form 8854 as Initial and final , with a note explaining the reason for missing the original filing back along with your tax return for the year of filing I-407.
( b) or call IRS or visit the IRS office ( generally there is one in the embassy of US in each country ) and ask for help for this oversight.
Note that there is always a risk that IRS would take the position that while you had abandoned Resident status ( from an immigration standpoint ) you still remained a Resident for Tax purposes , implying that they have right to tax your world income. I don't believe they would especially if your current tax home is in a country with a Tax treaty with US.
Personally I prefer option (b) if possible first and then follow up with option (a) or whatever the IRS suggests.
Is there more I can do for you ?
I am sorry I could not provide a lot of good news on this.
pk
