S.21 Notice - Date served/date of service Forms N5B and N215

Hi - I have carried out research, using this very useful forum, on how to complete a claim for possession using the accelerated procedure Form N5B.

I am happy with my completed form except for Question 5. I sent a S.21 notice, dated 12 February 2013 (expiry date 25 April 2013, using 1st class post. The tenant returned an acknowledgement of receipt dated 14th February, which happens to also be the date of deemed service.

Question 5 of form N5B requires a date - 'On the ???????? a notice in writing, saying .... was served......' I am not sure if I enter the date of the S.21 Notice, i.e. 12th February, or the date of deemed/actual service, i.e. 14th February. Can anyone please clarify the date I need to enter.

PS - I note that the Form N215 'Certificate of Service' has 2 dates, i.e. 'On what day did you serve' and 'The date of service is'. I assume these are 12th February and 14th February.

Thanks for any help.