"New" players appearing on player comparison list

My apologies if this is a banal issue. I have tried to search for an answer, but cannot find it on forums or on the web.

When I go to the player comparison tab, and select my team's player list, I notice there are four "new" players, which aren't signed by the club (nor even for trial).

All these four players are goalkeepers, and all of them are between 16 and 17 years old.

There hasn't happened any youth intake this season yet either (and the youth intake predicted date is one month or so away).

Also, none of them are regens (or, at least, they don't appear to be).

I can check these players' data (only overview, stats, comparison) and they appear to be fully fit, despite never appearing in match.

Apparently, I can offer them contracts.

Any idea of why this happens?

Thank you very much!