The majority of scholars said that it is not permissible to fast on the Days of Tashriq whether it is an optional fast, making up a missed fast or fasting in fulfillment of a vow. So, the fasts that you observed on the Days of Tashriq to make up for missed Ramadan fasts, are not valid, and you must repeat them.

It is not permissible to delay making up missed Ramadan fasts until the next Ramadan comes without an (valid) excuse. If a person delays that, then he must offer the fidyah: feeding one poor person for each day.