1) My account's username and it's meaning.
Unlike the other accounts, it's clear for anyone who knows football that this username means something to me and isn't random as the usernames for the other users are. In the post linked below, I make a joke about England and the world cup, and I spoke of how I want an English team to win the UCL. That on itself means nothing but when you realize that my username was modeled from the name of a young English player then it's clear that some amount of thought went into my username as opposed to the others.
Maybe that's because your account was created first and was made to be the "main one". The sockpuppets came later (which is confirmed by the dadets of creation) and their names weren't so thoroughly thought through. Making 2 posts with a reference to football in a period of 3 weeks doesn't really change anything.
If whoever I'm accused to be an alt of is a massive Chelsea and England fan as I am then it's okay to be suspicious but I'm sure that whoever I'm accused of being an alt of doesn't even watch the EPL.
These accounts are too new and have too few posts to draw conclusions.
2) Registration dates.
If we look at the registration dates of the other accounts that I should be connected to, there are clear differences that should raise flags. Of the three other accounts, one was created on the 8th of April and the others were created on the 11th of April. My account on the other hand was created on the 26th of March.
Too short of a timespan to use it as proof in your case. Who told you that all socks have to be registered on the same day?
3) Forum behaviour.
If you take a look at the post history of the other users, you'll see (...)
Your post history is almost non-existent. There's not enough data to paint a picture.