Hello - new here

I look forward to reading all the interesting posts....
But first -
I've been served with a Section 21(b) Fixed AST notice. The managing agents delivered it by hand, but not to me in person. I found it on the floor.
1. It's dated late therefore the two months notice is up after the end of the six months tenancy period.
2. I think it may be invalid because the notice expiry date doesn't have the words:
'after xxxxdate' on it. It's just the date the landlord wants me out.
I've read that the expiry date must NOT be the date or before the date of the end of the tenancy agreement period. ie - if the tenancy ends on 30th November the expiry date should read "AFTER 30th November."
3. I don't know what my rental period is. The rent was paid in advance.
4. My name is on it, but not my address. (although the address of the property is on it in another box.)
5. The manager of the letting agent has asked me to leave before the two months notice is up and has offered me incentives to go. I can't go for very complicated reasons.
I've looked things up on the net, but advice seems conflicting....