The most notable departure was Marcus Harness, who moved for an undisclosed fee to rivals Ipswich just weeks before the opening games of the season.
Meanwhile, Aiden O’Brien, Shaun Williams, Callum Johnson, Ollie Webber and Paul Downing all departed for free.
As well as those names, Cowley’s five loan signings also returned to their parent clubs upon the expiration of their deals.
With another turnover of players expected in the upcoming window under John Mousinho, how have last summer’s exits fared since their Fratton Park departure?
Here’s how this season has unfolded for those 12 players.
9. Alex Bass
The keeper fell out of favour with Cowley, which saw the arrivals of Josh Griffiths and Josh Oluwayemi. Bass made the move to Championship side Sunderland in July for an undisclosed fee but is yet to feature in the second tier for the Black Cats. He’s made just two outings in cup competitions, while also scoring for the under-21 side in October. Photo: Dennis Goodwin
10. Shaun Williams
After a difficult year at Fratton Park, which saw the midfielder fracture his back, he was released at the end of his deal. He made the drop to League Two Gillingham, where he’s appeared 35 times for Neil Harris’ men and has played a key role in their survival hopes. Photo: Jason Brown
11. Mahlon Romeo
After his season-long loan spell from Millwall came to an end, Romeo brought his seven-year affiliation with the Lions to a close in the summer. This saw him join Championship rivals Cardiff and has gone on to amass 24 outings for the Bluebirds. Photo: Jason Brown
12. Hayden Carter
There were plenty of calls from Pompey fans to break the bank in order to bring Carter back to Fratton Park after his loan expired. The centre-back remained at Blackburn and has emerged as one of the most promising talents at Ewood Park, where he’s impressed in 22 Championship outings this term. Photo: Graham Hunt