Not sure, UEFA and FIFA seem to have a different idea.
At least these parts suggest players have to be registered for the club they are playing for
and also be registered only for 1 club at a time.
That's why loans outside our FA don't add to HG calculations.
"UEFA rules, page 40:
https://www.uefa.com/MultimediaFile.../Regulations/02/55/82/79/2558279_DOWNLOAD.pdf
43.02 Each player must be duly registered with their national association as playing for the club concerned
in accordance with the association’s own rules and those of FIFA, notably the
FIFA Regulations on the Status and Transfer of Players.
FIFA rules, page 10:
https://resources.fifa.com/image/up...2018-2925437.pdf?cloudid=c83ynehmkp62h5vgwg9g
1. A player must be registered at an association to play for a club as either a professional or an amateur in accordance with the provisions of article 2.
Only registered players are eligible to participate in organised football.
By the act of registering, a player agrees to abide by the statutes and regulations of FIFA,the confederations and the associations.
2.A player may only be registered with one club at a time."
Angelino has been registered for more than 36 months at City (season 2013/14, season 2014/15, Oct '15 - Dec '16) before turning 21
https://www.transfermarkt.co.uk/angelino/profil/spieler/277179
(without loan spells outside England and Wales)
and counts as club trained homegrown IMO.