Section 1.909-4 - Coordination rules(a)Interim rules. The principles of paragraph (g) of § 1.909-6 apply to taxable years beginning on or after January 1, 2011.(b)Effective/applicability date. This section applies to taxable years ending after February 9, 2015. See 26 CFR 1.909-4 T (revised as of April 1, 2014) for rules applicable to taxable years beginning on or after January 1, 2011, and ending on or before February 9, 2015.T.D. 9710, 80 FR 7332 , Feb. 10, 2015