Nottingham Forest prospect Fornah, 22, was a long-term target of the Shrewsbury Town boss, who revealed he held out until the final moments of the summer transfer window but was unable to bring Fornah from the City Ground.
Fornah starred once more yesterday, in his 13th appearance on loan at Salop, to help his side to a 1-0 home victory over Lincoln for a third League One win on the spin.
Cotterill, whose side climbed to 15th with the win, was honest at the end of last summer as a couple of targets got away from Town. Fornah, meanwhile, continues to grow into his Shrewsbury loan and has put in a handful of consecutive top displays.
"The only disappointment with Tyrese is that I didn't manage to get him in August," said Cotterill.
"I hung on and hung on and hung on and then he couldn't come out in the end, that's a disappointment.
"We didn't have him four or five months earlier, he was the one I was waiting and waiting for and it just couldn't happen for one reason or another.
"And now it has happened we're seeing the benefits of it."
Town instead took Leicester midfielder Khanya Leshabela on loan for the first half of the season but the South African struggled to make an impact.
Fornah arrived in Shropshire after little first-team football for his Championship parent club. He had been involved with their under-23s set-up and checked in low on minutes and match sharpness.
The midfielder is very well thought of by the East Midlands club, with whom he signed a new long-term deal in recent months.
He grasped the opportunity at the heart of Shrewsbury's midfield following the unfortunate injury to David Davis sustained against Portsmouth a little over a month ago.
Fornah said of yesterday's hard-fought victory in the spring-time heat: "The first half was a bit tough, but once we came in we said as a group that once we get going physically not many people can handle us.
"The second half was a performance we should give.
"Every game means a lot to me. I want to come in and do well, not just for myself, but for the gaffer who believes in me and the club as a whole and the fans.
"It was a bit slow, the game as a whole, but when we had the ball we tried to make good use of it.
"The gaffer says to me I've got to keep doing what I'm doing, giving my all for the fans."
Daniel Udoh was Town's match-winner once more as he thrashed in a late low winner for his 15th goal of the season six minutes from time.
"I've never seen a player so strong off both feet, it's a joke," Fornah said of the top scorer.
"Dan's got that quality, it's just about confidence with him. When I came in he had a bit of a drought but us as fans and as a club we've got to believe in the strikers and give them confidence.
"There will be games when they play well and don't get a goal but as a team we have to take pressure off them, as the gaffer's been saying."