My last entry into Thailand was on a non 'o' single entry visa which was good for 90 days.

At the end of the ninety days I went to immigration to get a one year based on marriage but didn't have all of the required paperwork so I settled for a 60 day extension instead.

As we were leaving the office, the immigration officer told my wife that I needed to come back and see them before the 60 days were up "if I wanted to keep my non 'o' visa valid".

I thought that once I'd entered with it and used up the 90 days then that was it, visa finished, so I'm a bit puzzled as to what he meant.

He emant that you cna still get a 1 year extension of stay, provided that now your documents are in order.

You visa was finished as soon as you entered the country.

What the officer meant was you needed to come back and apply for the one year extension of stay before the 60 days ended.

Ok, thanks for the replies

And you can apply for an annual extension of stay at most immigration offices up to 30 days before your current permission to stay expires - and even up to 45 days in advance at some offices (e.g. Chaengwattana & Jomtien). You won't lose out by applying early since your extension will still be dated from the expiry of your current permission to stay regardless.

And sooner rather than later is better IMHO, particularly for your first extension, to give you sufficient time to iron out any problems which might arise. That said, you won't, of course, be able to apply until the initial 60-day seasoning period for the 400,000 THB minimum balance in your bank account (assuming that this will be your method of proving finances) has expired - was this at the heart of the paperwork problems to which you referred?