What is the real position on entering Thailand visa exempt, and are there any restrictions?

*** There is no "reset".

*** There is no mention of "calendar year".

*** There is no two-times limit on visa-exempt entries within a one-year period.

In case you have heard such drivel from out of the mouth of an Immigration officer, this officer will soon learn that what he said just can’t be true.

What actually counts is: There are only two extensions on visa-exempt entries possible, within a 1-year period.

The first extension will be issued for 30 days, the extension for a second visa-exempt entry will be issued for 7 days

You can theoretically do 4, 5 or even 6 visa exempt entries for short 2-3 weeks holidays, within a one-year period, if you never maximize each stay.

Of course, upon each entry, you should be able to proof your onward travel, a few nights of a booked accomodation and proof of cash equivalent of 20,000 THB

You should refrain from thinking in terms of "calendar year"

I would rather say that all visa-exempt stays within the recent "1-year period" will be considered when you attempt another visa-exempt entry

Just think about it, if a “calendar year” count would be in effect:

This would allow 157 days BEFORE New Year, and 157 more days AFTER New Year, totaling in a 304-days consecutive visa-exempt holiday inside Thailand.

The mind boggles.

Do you really believe that a Thai Immigration officer in January or February looks up the amount of visa-exempt stays within a "calendar year" (none yet) and ignores all the days of your visa-exempt stays within the previous year?

It won't make much sense.