I'm curious what the various sanctioning bodies state about the dates on seatbelts ? I'm sure they are different in the various divisions, so based on the manufacturing date, how long are they usable for ?

Typically 2 years for an SFI certified belt. I believe the FIA certified belts are good for 5 years.

Sorry Stupid question...
If the belts has been in new sealed bag and new box for long time, Still have to replace? Could re-inspection by sanctioning bodies state ?

What about head and neck restaint (HANS)? I have one and have not touched it since 1997. I used once in dirt track local.

The answers depend on the sanctioning bodies you are racing with. Last year, if I remember right, NASA has us get our older HANS devices inspected by authorized dealers or HANS to get an FIA sticker.

Belts like you have are likely ok for a HDPE day or autox, no sanctioning body will let you use an expired belt for competition.