I am booked to leave Suvarnabhumi on 3 March 2014 at 20:40. I arrived 5 December 2013. The "ticket" in my passport provided by immigration states that the 90 reporting date is 4 March 2014. I have worked out that this is correct counting the day of arrival as one day. I have a multiple re-entry permit. I return early April and the retirement "visa" expires 1 June 2014.

I did not plan this and it would seem to me that I do not need to report to the local immigration office before I leave.

Since you are leaving before your report is due you do not need to do it.

Your next report will be due 90 days from your arrival date including that date in the count.

No problem and no need to report. The 90 day report clock will reset when you return in April.

...and it will not reset when you get your next extension in May. So, your next 90 day report will be early July.

Thanks for the confirmation. It is important to remember that my 90 day reporting will be counted from when I return and not from the date I get my retirement visa extension at the end of May.