The maximum prepaid expiry here for "standard" SIMs is 365/366 days; tourst-y SIMs may have a shorter expiry, like 90 days.
Most providers have a 90-day usage requirement, which may or may not be enforced.
There are many, many, many methods to extend expiry - all of which have been detailed within this thread multiple times. Individual top-ups, for as little as 10 baht each yield 30 days.
There are top-up machines everywhere, they are easy to use, and a 10 baht top-up costs 12 baht, so 144 baht for 360 days, with 120 baht credit.
https://www.google.com/search?q=boon...w=1920&bih=938
DTAC does allow for expiry extension via USSD or IVR methods, with some "rules. This feature may be embedded in the DTAC app? Or available on the web-management portal?
https://play.google.com/store/apps/d....android&hl=en
https://my.dtac.co.th/esv/en/login
DTAC Call is also an interesting app, offering WiFi calling and management of multiple numbers.
https://play.google.com/store/apps/d...ac.wificalling
Jai Dee Services | dtac
See "Day-Giveaway", essentially 2 baht fee for every 30 days.
dtac prepaid self-service numbers | dtac
TrueMove H used to have a similar scheme,
Validity Extension Service for Prepaid Customers by TrueMove H TrueMove H ? Mobile Package, Devices, and Deals
AIS also has something similar (Mao Mao) but not really the same - +30 days with some calling credit.