Home Grown Status

Ok, just need some help clarifying this. So as far as I can tell, if I buy a player at 17 he will end up classed as home grown. But is it 3 seasons or years to be home grown?

For example, if I bought an 18 year old at the start of the season, will he still become home grown for his 3 seasons before 21 or does it have to be 3 years, i.e. does he have to join the club no later than his 18th birthday?

If it is 3 seasons, then does it have to be full seasons? For example an 18 year old bought in the January window, would he still make it as a home grown player?

The reason I need to know is mainly to help fulfil champions league registration rules, since I don't have enough HG players atm and can't find any that I want to buy or are cheap enough for their age (I don't like buying older players).

Also a lot of the better players are coming from South America, where they can't leave before they're 18 and if their birthday doesn't fall in a transfer window I need to know if they can still be home grown.

Apparently it's different on FM11 from what i've noticed, you need to sign the players before they are exactly 18 or it won't count.

Not sure how it works with non-EU players though.. sometimes they'll count as HG and sometimes not but i don't really know why.

Hmm, that's a shame, just signed a very promising Argentine a couple of days after his birthday, fingers crossed that'l work out HG though.

Another thing I just wondered, do season loans abroad detract or still count as trained by club?