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.
1. George Hirst
The striker was tipped with a return to Pompey following his impressive loan stay last term. He spent the first half of the season with Blackburn before Leicester cut his temporary stay short in January and instead sent him out to Ipswich. He’s scored one goal in 10 appearances in all competitions for the Tractor Boys. Photo: Paul Thompson
2. Ollie Webber
Webber failed to register a competitive outing for the Blues during his six-month stay where he was second choice to Bazunu. After being released by Pompey, the 22-year-old returned to Northern Ireland, where he penned a 12-month deal with Premiership side Glentoran. Photo: Jason Brown
3. Aiden O'Brien
Although Pompey offered the striker fresh terms to remain beyond the summer, he opted to make the switch to League One rivals Shrewsbury. However, his time at Salop was heavily affected by injuries - limiting him to six outings from the bench in the league. In January, the former Millwall man made the drop to League Two strugglers Gillingham, where he’s yet to net in five appearances during his loan stay. Photo: Jason Brown
4. Tyler Walker
A loan spell from hell for the striker, scoring just once in 15 league games for the Blues. Despite being given a fresh start by Mark Robins at the start of the season, Walker has made just one appearance in the Championship since November and was tipped with an exit in January. His current deal with the Sky Blues expires in the summer. Photo: Nigel Keene