Versions of 26 CFR 1.66-5 - Effective date on LawServer 2024 26 CFR 1.66-5 – Effective date 2023 26 CFR 1.66-5 – Effective date 2022 26 CFR 1.66-5 – Effective date 2021 26 CFR 1.66-5 – Effective date 2015 26 CFR 1.66-5 – Effective date 2014 26 CFR 1.66-5 – Effective date 2010 26 CFR 1.66-5 – Effective date 2009 26 CFR 1.66-5 – Effective date.