My understanding is the DTV is a 5 year multiple entry visa. What needs to be extended before 5 years has past other than leaving the county within 180 days before returning?
If you stay 90 days, reporting to immigration is required under current law is my understanding.
TLDR : Answer Summary
The DTV is a 5-year multiple entry visa for Thailand. To maintain this status, you must leave the country within 180 days of your last entry unless you extend the visa at an immigration office. Additionally, a mandatory 90-day reporting to immigration is required for all visa holders.
DTV VISA RESOURCES / SERVICES