Receiving a section 21(1)b

My daughters landlord has served her with a section 21(1)b Notice to quit as they are selling the house.

Her fixed six month tenancy ends on the 8th of February 2014 so the notice has been issued during the fixed term.

The notice was dated 19th Jan and delivered on the evening of the 21st Jan through the letterbox. 

The section 21(1)b notice states that possession is required by the 21st of March 2014?

The question I would like to ask is, as her fixed tenancy started on the 9th of the month and therefore ends on the 8th of the month shouldn’t the landlord have dated the required possession date as being the 8th of April (rent payable monthly in advance).

Also as the tenancy will be periodic from the 9th of Feb shouldn’t he have issued a Section21(4)a instead of the section
21(1)b

Many thanks

Annette Tolley