Hey

In most cases the NCL Certificate is valid for a time period of one year after it is issued hence I do not think that your certificate which was produced 2 years ago is valid now however if you are sure that it was a NCL Certificate for 3 years then you still have one more year until that certificate elapses. In most cases the ncl  certificate has to be renewed every year.

Also, to be classified as out of NCL and into the creamy layer the salary (per annum) must exceed the minimum amount set by the government for 3 consecutive years, that means that to be considered not an obc ncl your father must have an annual income of more than 8 lpa for 3 years.

I will suggest you to consult a practitioner of law before going forward. You might find this useful- http://www.ncbc.nic.in/Writereaddata/Report%20on%20Income%20Criteria%20for%20Creamy%20Layer%20-Pandey635817940067450735.pdf