What was Southampton's defence like when they had that defence that we're about to make ours? Did they ever have Clyne, VVD, Lovren and Betrand at the same time?
Nope. Only two out of four played together in any season.
12/13: (60) Shaw (then 17),
Clyne (then 21), Fonte; all three were in the Premier League for the first time
13/14: (46) Shaw,
Clyne, Fonte,
Lovren, Wanyama
14/15: (33)
Clyne, Fonte, Wanyama,
Bertrand, Alderweireld (loan), Forster (goalkeeper)
15/16: (41) Fonte, Wanyama,
Bertrand,
Van Dijk, Forster (out for half a season)
16/17: (48)
Bertrand,
Van Dijk (out for half a season), Forster; Fonte left in January
Also, here's an interesting tidbit:
In 12/13, Southampton had conceded 40 goals in 22 games in their first season back in the Premier League when they sacked Nigel Adkins. Under Pochettino, they conceded 20 goals in 16 games for the rest of the season, which included games against 9 of the teams which finished in the top 10 (they finished 14th).
The interesting bit is that their goals allowed rate didn't change much in 13/14 versus the second half of 12/13 (46/38 ~= 20/16) even though they added Lovren and Wanyama, and with Shaw, Clyne and Fonte now having played a season in the Premier League.
Their defensive record did take a big jump in 14/15 - after they swapped Koeman for Pochettino (to Spurs), Bertrand for Shaw (to Man Utd), Alderweireld on loan for Lovren (to Liverpool) and Forster for Boruc (on loan to Bournemouth in the Championship).