Kilpatrick has it wrong. He (or worse someone at the club) doesn't understand club trained
Here's the official pdf (relevant section starts on page 40)
43.02
No club may have more than 25 players on List A during the season, two of whom must be goalkeepers. As a minimum, eight places are reserved exclusively for "locally trained players" and no club may have more than four "association- trained players" listed on these eight places on List A. List A must specify the players who qualify as being "locally trained", as well as whether they are "club- trained" or "association-trained". The possible combinations that enable clubs to comply with the List A requirements are set out in Annex H.
So a maximum of 17 non locally trained
43.04
A "club-trained player" is a player who, between the age of 15 (or the start of the season during which he turns 15) and 21 (or the end of the season during which he turns 21), and irrespective of his nationality and age, has been registered with his current club for a period, continuous or not, of three entire seasons (i.e. a period starting with the first official match of the relevant national championship and ending with the last official match of that relevant national championship) or of 36 months.
A club trained player can be an 18 year old who has been at the club 3 seasons
43.05
An "association-trained player" is a player who, between the age of 15 (or the start of the season during which the player turns 15) and 21 (or the end of the season during which the player turns 21), and irrespective of his nationality and age, has been registered with a club or with other clubs affiliated to the same association as that of his current club for a period, continuous or not, of three entire seasons or of 36 months.
An association trained player can be an 18 year old who has been at an English club for 3 seasons
Now to the B list
43.10
Each club is entitled to register an unlimited number of players on List B during the season. The list must be submitted by no later than 24.00CET on the day before the match in question.
43.11
A player may be registered on List B if he is born on or after 1 January 1996 and has been eligible to play for the club concerned for any uninterrupted period of two years since his 15th birthday by the time he is registered with UEFA. Players aged 16 may be registered on List B if they have been registered with the participating club for the previous two years without interruption.
So a B list player has to have been at the club for 2 years!
So taking our squad from
https://www.premierleague.com/news/465277
Alderweireld, Toby Albertine
1
Aurier, Serge
2
Davies, Benjamin Thomas
Association-trained player
Dembele, Mousa
3
Dier, Eric Jeremy Edgar
4
Eriksen, Christian
5
Gazzaniga, Paulo Dino
6
Heung-Min, Son
7
Janssen, Vincent Petrus Anna Sebastiaan
8
Kane, Harry
Club trained player
Lamela, Erik
9
Llorente Torres, Fernando Javier
10
Lloris, Hugo
11
Nkoudou Mbida, Georges-Kevin
12
Rose, Daniel Lee
Club trained player
Sissoko, Moussa
13
Trippier, Kieran John
Association-trained player
Vertonghen, Jan
14
Vorm, Michel
15
Wanyama, Victor
16
Under-21 players (excluding players out on loan, sorted by age to make it easier)
Harry Winks
Club-trained player Also eligible for B list
Dele Alli
Association-trained player Also eligible for B list
Davinson Sánchez
17
Joe Pritchard
Club-trained player Also eligible for B list
Luke Amos
Club-trained player Also eligible for B list
Anthony Georgiou
Club-trained player Also eligible for B list
Kyle Walker-Peters
Club-trained player Also eligible for B list
Shayon Harrison
Club-trained player Also eligible for B list
Ryan Loft
Club-trained player Also eligible for B list
Christian Maghoma
Club-trained player Also eligible for B list
Juan Foyth
18
-stopping here but there are plently more eligible for both lists
We can make up our 8 locally trained with 3 association trained (Davies, Tripper and Alli) and 5 club trained (Kane, Rose, Winks, Walker-Peters and Georgiou)
That leaves the club with 17 places for 18 players non locally trained player.
The obvious one to leave out is the 3rd keeper.