A section 21 notice arrived for me from my landlord today. It gave two months notice from the date on the letter, but has been delayed in the post by a couple of weeks, so I'm actually only getting about 1.5 months notice. Is it still valid? I've found something on Thetenantsvoice.co.uk saying that "Do note, that the start date is when the notice is served to you, not when the landlord has drafted it." - does that mean I've not been given the required amount of notice?