It's hard to say for such a long time. The key is whether there is a record of you 1988 to 1995 in the social security bureau system. Besides the fund handbook, can you provide any other evidence to prove that you paid insurance in that year? If so, you can ask the Social Security Bureau to confirm the payment records of those years with other evidence.

Since there is a way to make up for it, you can make up for the retirement period after making up for it. I suggest you make it up.

Of course, if you don't retire so soon, you can also look for notices everywhere and ask the unit to issue a signature that you received 336 yuan. If the unit can't get out, you can always find the superior department in charge. As long as the loopholes in the management of the unit are found, you can ask the higher authorities to be responsible.