attendance date of my BS and MS course

I have completed my graduation from Bangladesh. And i am applying for graduation study at USA. All of the universities mentioned to write the attendance date of my BS and MS course. But there are not any official record with me and even in my certificate. But i can see in my certificate "publish date of results" and session mentioned. The university where I studied took 6 years to complete 4 years course. Now what date will I write there?

Will I write what I assumed ?