I think there is an additional consequence, which is that you may not be able to get a tourist visa at some embassies / consulates in the region with an overstay stamp in your passport.
At the moment I have only heard of one that this applies to but that may change in future.
you shouldn't need the Thai insurance to do those things because your visa was issued before the new requirement came into force.
That is how it should be and how it has worked for many people.
However, not all immigration officers enforce the same rules and it hasn't been that way for everyone.
Carry a copy of your travel insurance certificate and if asked tell them you have insurance but because your visa was issued before October 31st 2019 you don't need it.
Hopefully there will be no further problem but if they and their superior officer still require Thai insurance they *should* stamp you in for 30 days so you can buy insurance (at least this is what they have been doing).
If you arrive on the 28th of January and leave on the 26th of February 2020 you will have the option of doing nothing or going to your local immigration office as detailed below.
If you arrive on the 27th of January you will need an extra day.
You should go to your local immigration office and tell them that you were stamped in incorrectly.
They should correct your stamp to a 1-year stamp.
It may also be possible to extend the 30-day stamp for another 30 days, just like a normal 30-day stamp. However, I have no idea if it actually is possible and I don't remember seeing reports of anyone trying it.
Nothing is certain. While a number of people have had their stamps corrected that way, one person recently posted about being refused the correction Chiang Mai immigration.
How pre-October 31st 2019 O-A visas are handled seems to be down to the luck of the draw but with the odds in your favour... at the moment. Tomorrow might be different.
Keep an eye on this group or ask again before you return.
Truly unfortunate but thanks for updating the group.
I like Tod's advice to try getting a 1-year stamp by crossing the border and as he said even if you only get another 30-day stamp you'll probably need that time to get the insurance.
You don't say where you are at the moment but you posted back in August asking questions about getting an METV, so would it be correct to assume that you are currently in Asia and are looking for the best embassy or consulate to visit for another SETV?
Your 2 land border 30 day visa exempt entries per calendar year reset on the 1st of January but that is no guarantee of entry.
Your entry history does not reset and will be visible to the immigration officer at the border. However, entry and visa histories are not yet visible to the embassies or consulates although anything in your passport is visible (and they *may* also have a record of past applications at that location but I don't know if this is the case).
There is no limit for tourist visa entries by any method or visa exempt entries by air but even though the law does not specify it, you should consider that if they feel that the person standing in front of them may be trying to live in Thailand on tourist visas the liklihood of denial increases.
There are limits to how many tourist visas an embassy or consulate will issue but these vary and the numbers appears to be in flux.
A number of immigration officers appear to be imposing a 6 months in the last 12 limit on tourists and as James Miller mentioned above you spent 6 months in Thailand in 2019.
An easy land border may be better than air since you will just have to walk back to the other country if you are denied.
If they require any additional documents they will either tell you at the embassy when you submit your application e.g. if your bank statements do not have the right information or they will call or email you later (they are quick so they may contact you the same day).
As others have suggested, you can get an O-A visa from your home country and leave your cash at home. You *may* be able to use any existing foreign health / travel insurance for the first year (maybe also the second with a re-entry permit) or you could buy the Thai health insurance.
You ruled out proving your income in your original post. However, the income method also includes the option of transferring at least 65,000 per month into the country from abroad, if you are unwilling or unable to prove your income by the other allowed methods.
Is the monthly transfer option something you have considered? The money doesn't have to remain in the bank so you can use that money live on.
1) Go to your local immigration office and try to have them "correct" the stamp (others have had success with that approach).
2) Buy the Thai insurance and be done with issues for a year.
3) Leave then try to enter again without insurance (maybe at a different entry point) and hope that you succeed, even with the 30-day stamp, which may have an annotation in Thai about a lack of insurance.
4) Same as (3) but buy travel insurance to show. Now your risk may be lower than in (3) but your costs would be higher and with no guarantee it would work.
5) It may be possible to change passports and abandon your current O-A visa and get a different visa but I'm not sure about that. Others may know.
6) Find a foreign insurance company that is willing to fill out the foreign insurance certificate on the site Robert Lagas linked to and buy insurance from them. Immigration officers should accept that certificate as proof - *this is speculation on my part* - but since that form is good for people who are applying for O-A visas now, it should work for you too.
I'm not sure if there are any other options for you until your visa expires.
I would try (1) first. If they refuse then look at other options.
If you decide to go for (2) and don't really want health insurance for some reason, I understand that Pacific Cross have plans which can offer steep discounts for high deductibles.