Effective date of agreement.

Please advice if case of any agreement with company & service provider, Which date will be considered as effective date of agreement either on the date it got made, signed & stamp paper issued or the effective date mentioned on agreement. Its matter of non compete. I have dealt with their customer before the agreement got signed but the effective date they mentioned in agreement is in past. Also I was out of India when this agreement got signed. Will it be treated a valid agreement or not since I have not signed as a director of company.