From and after such filing the creation of the district shall be complete and its existence cannot thereafter be legally questioned by any person except the state of Washington in an appropriate court action brought within six months from the date of the order of the county board tabulating the abstracts of the returns of the organization election and creating said district. If the existence of said district is not challenged within the period above specified, the state of Washington shall thereafter be forever barred from questioning the legal existence of said district by reason of any defect in the organization thereof.