What I have learned is:

After being sentenced, retirees do not enjoy basic pension benefits during their prison term. According to the "Reply on Retirees Being Sentenced to Criminal Detention and More Penalties Related to Pension Insurance Treatment", retirees do not participate in the bookkeeping and calculation of basic pension personal accounts during their prison terms.

However, once the retirees are released from prison, they will resume their basic pension benefits before serving their sentences. According to the relevant regulations, retirees can continue to receive the previous basic pension after serving their sentences. This means that they can continue to receive the original pension benefits.

Although retirees can't enjoy basic pension benefits during their prison term, they still have the right to apply for other related social security benefits. For example, they can apply for social benefits, temporary relief funds, etc. to help them tide over difficult times.