4 Pa. Code § 243.7
Those members with accrued social security integration credits on March 1, 1974, may continue to earn Social Security integration credits until service is terminated. Those members in continuous service who terminate after March 1, 1974, may continue to accrue Social Security integration credits if they return to active membership in the System within 6 months, provided they have not withdrawn their accumulated deductions. Those members who have vested, or are in receipt of an annuity, and return to State service after March 1, 1974, shall have their Social Security integration credits restored, to the extent previously earned, and may continue accruing Social Security integration credits for service rendered thereafter.
Social Security integration credits may be restored only to the extent allowed in this section. In all cases, Social Security integration credits shall not be available for any State or nonstate service applied for and purchased after March 1, 1974, regardless where or when the service may have been performed.
4 Pa. Code § 243.7