Is it permissible, in Islamic law, for a retiree to accept and receive sums of money as differences for a distinction allowance and rest allowances, which the company approved retroactively after his retirement?

There is no sin upon you in accepting these sums, as long as the specialized committee has recommended it, for they are more knowledgeable about the entitlements of the company's employees. You can ask the committee about any of these entitlements that are unclear to you.