Key with Expiration Date vs Register After + Nbr Days

[educdz]

Hello,
i'm wondering what's the difference between register a key with Expiration date or to create a key with Register After + Nbr Days?
Thanks

[Enigma]

Hi, the number of days counter starts from the first run of the software on a particular computer. So the date of exiration is undefined.

However the expiration date is always the same.

[educdz]

let's take this example as showed in the attachment:
What's the difference between
1-
Register with a key with: Expiration date of 31/03/2016
Or
2-
Register with a key with: Register after 31/03/2015 with limited days of 365 days
3-
Register with a key with: Register Before 31/03/2016
?
For me it seems like they're all the same? if so can we use the combination of all of them? for more security?
thanks