How university maintains their old certificates

Universities will never destroy purposefully any record of the students. They will have the records kept both in physical form and digital form also. They will maintain a record of all their students with identification to each student. Not only universities but also other educational institutes will also maintain the records.
I passed 10th class in the year 1970. I lost the certificate. I applied for a duplicate in the year 2010. That means almost after 40 years. I got the same from the board.
In your original marks sheet gave for correction. When you got it back there are some other mistakes are there. Did you have a copy of the old certificate with you. Make a letter to the university giving the complete information and attaching a copy of the old certificate and original new certificate and send it to the university by registered post. Keep a copy of the letter along with all the copies of the attachments, the receipt given in the post office for the registered post and the acknowledgement copy you received for your future reference. It is advisable to personally go to the university and meet the concerned people. Then the work will be completed fast. Otherwise, it will take a long time. If you personally go you can explain the problem to the concerned clearly. After that, the University administration will do the needful and give you the corrected certificate.

All the universities take care of the documents of their students and hence even if there is a lapse of forty years, you can find your relevant documents if you request them to have a copy of the same in case of misplacement or otherwise.
Since you have despatched your original mark - sheet to the university for the correction purpose and still you find several mistakes in the mark - sheet.
To solve the same, there are two ways either you meet them personally along with other documents proving that you had passed out the same examination or you should write an application indicating the anomalies found in the corrected mark- sheet and along with that application enclose the prescribed fee in the form of demand draft. Send your application coupled with the demand draft to the concerned official so as to get a fresh copy of the mark - sheet. You should attach an acknowledgment card along with your envelop so that the card reaches to you after getting the initial of the appropriate authority. You may retain the same as an evidence of your initiative. However, the former rout would take less time.