An HSA is a trust. Although I don't know specifically about South Dakota law, in most states a trust is considered established on the date when funds are first placed in the trust. In the case of an HSA, the establishment date would then be the date on which the first deposit was made to the HSA account of an HSA-eligible individual.
A transfer of the HSA does not change the establishment date for your HSA. The establishment date of the original HSA carries over to the new HSA.
