Thank you everyone fo your suggestions. I have found a solution that suits my situation and my budget.

TIT - This is Thailand. It will always involve money to oil the wheels but there is always a compromise solution to be had.

Also, better to count the days (60) - not the calendar months (2). Why because February is only 28 - some have slipped up over this with a pedantic officer. Yes, I know, now I'm being pedantic. When in Rome.

For what it's worth - a personal visit (although tiresome) is still the most effective and responsive way to go. Queries can be explained, confusions can be clarified, issues can be resolved. The vagries of your local Immigration office become clear. As has been said many times, they are not all the same. Plus, the online systems, whilst admirable in intention, do not work for all situations. Often, courtesy and humour can go a long way in a personla visit.

@Tony *******

ko chai kab. Employer promises cancellation letter (PDF) will forwarded same day. So all should be smooth. Thank you.

@Benjamin *****

yes sorry non-B extension (for work) to non-O extension (for marriage). Was previously on marriage visa (same woman / same address) but had to change when started working.

Given all that - if still no complications - thanks for your reply.

@James *******

I know ...

Is there some way of clearly highlighting the difference between a 'visa' and an 'extension of stay'. Even though it is clearly stated on stamps in their passport, so many people don't seem to get the implications when asking questions about changing their status. So wearisome for moderators and readers. Appreciate that the 'ins and outs' can be confusing - but it's not rocket science. I do not expect this post to make it through.

The second document you speak of is a photocopy of the marriage registration entry in a large inventory kept at the Ampeur Muang offices of where you got married (i.e. the district admin offices). They gladly give you a copy for a few Baht. The wait might take a while. This confirms the issue of the 'Certificate' you already hold.

If you go out (good luck) 90 day reporting gets reset from the day of rentry.