Just back from Oz with Non-O (Single Entry)

Now after getting a bank a/c 800K seasoned 2months then 1yr extension ( based on Retirement) am I correct in understanding I still need to leave Thailand when current Visa expires 28Apr?

Thanks in advance

No. You have around 12 months before you have to leave or apply for another extension.

No, because the extension is an extension of the original stay.

Go by the stamp they gave you when you did the extension.

Don't forget you'll need to do address reports if you stay here 90 days.

...am I correct in understanding I still need to leave Thailand when current Visa expires 28Apr?

Once you get the extension of stay, you are legally in the country based on the extension until the extension of stay "must leave by" date show on the hand stamp you'll get at immigrations... normally one year for a retirement extension.

The non-imm O visa becomes irrelevant except for reference. Since the extension of stay only means you can stay IN Thailand (not cross borders) for one year (and the non-O visa will be dead), exiting Thailand and returning will require a re-entry permit to preserve your extension of stay.