UK Landlord Forum / Life

Hi
My tenant moved in and signed a tenancy agreement on 25.11.2011
I have served a section 21 as I want to sell the property
The date I put on the section 21 and handed it to my tenant is
24.03.2013 and it states that it expires AFTER 24.05.2013
Are these dates correct? I now have to apply to the court for possession using the N5B as my tenant is still living in the house I wish to sell
I just want to make sure the section 21 is dated correctly before I start court proceedings