Musiala is now one of the biggest stars in European football with Bayern Munich and Germany, while Colwill has established himself as a key player for Chelsea and England. Yet according to Robinson, both spent their childhoods living almost literally on Southampton's doorstep.
"The first thing is, now that I'm at Southampton, I was sat in St Mary's Stadium last week," Robinson told Football Presse.
"We had an Under-21 game and just behind the ground, literally I could see over the top of the stadium roof, is a block of flats.
"Levi Colwill lived in that block of flats and Jamal Musiala lived in the building alongside it.
"Absolutely overlooking St Mary's."
For Robinson, who is now responsible for identifying the next generation of talent as Southampton's academy recruitment chief, the story naturally raises one question.
"So the first question is, why didn't Southampton get them?"
The answer, he says, was a combination of Chelsea's excellent scouting network and the increasingly competitive battle for elite young talent.
"Chelsea got them through a very good scouting structure down in Hampshire led by a guy called Graham Castle.
"That was the first steal in a sense. It was Chelsea from under the nose of Southampton and just by good scouting."
Musiala would later leave Chelsea's academy for Bayern Munich, where he developed into one of the world's premier attacking players and became a key figure for Germany.
Robinson believes family ties and Germany's development pathway played a major role in that decision.
"Jamal's family were from Germany, I think. There was always that feeling that he might go back to Germany."
But Robinson says the modern academy landscape is now shaped as much by financial power as by development opportunities.
Recalling conversations with long-time Chelsea academy director Neil Bath, he explained how clubs were already struggling to keep pace with rising demands from elite prospects.
"I can remember Neil sitting and talking and saying, 'We can't just keep paying these kids more and more and more. We've got to have a structure. We've got to bring some sense to this because it's getting crazy.'
"He introduced tiers of payments to try and get some sort of structure."
Even so, some talents inevitably moved on.
"Jamal was obviously offered more to go elsewhere.
"Samuel Iling went to Juventus about the same time.
"You're going to lose some players if you do that."
According to Robinson, the situation has become even more extreme in recent years.
"Now under the new ownership and the new structure, they are offering amazing contracts to young kids.
"Kids are 17, earning £20,000 a week and they've never been in the first team.
"It is just crazy."
Robinson points to the current England youth setup as evidence of how fierce the competition has become.
"I went to watch England Under-17s a couple of weeks ago at St George's Park.
"The front three were Ryan McAidoo, Emil Heskey's son and Rio Ngumoha.
"Allegedly Rio's on £28,000 a week.
"He's only 17 and the boy's nowhere near the first team yet."
For Robinson, however, money is only part of the story. Elite youngsters are increasingly prepared to move abroad if they believe it offers a clearer route to senior football.
One example is Jamie Gittens, who has now completed a high-profile move back to Chelsea after establishing himself in Germany.
"I remember him at Reading where he was always a decent player, but not a top player at that point.
"But he got a great offer to go to Germany.
"And why wouldn't he?
"He's gone on and done well and he's had opportunity."
Ultimately, Robinson believes modern football has become a global marketplace in which even local talents can quickly be lost to bigger opportunities elsewhere.
"I don't knock the boys at all from going where the money's good," he said.
"But also where they think their careers can progress."
For Southampton supporters, though, there may always be a lingering sense of what might have been.
After all, two future international stars – Musiala and Colwill – spent their childhoods looking out at St Mary's Stadium, only to build their careers far away from the club that sat right on their doorstep.