Last week's historic announcement about gravitational waves came too late for a bet, placed by two physicists, that the discovery would happen before 2010.
But Prof Sheila Rowan and Prof Jim Hough said the seminal findings were "worth much more" than any winnings.
Both scientists are part of the Ligo collaboration that detected the waves.
Back in 2004, the pair placed a £25 wager at odds of 100/1 that Ligo - then in its first incarnation - would "detect gravitational waves by 2010".
"It was worth a punt," Prof Rowan told the BBC.
Betting agency Ladbrokes offered the wager alongside four other possible scientific breakthroughs, including the discovery of the Higgs boson (odds of 6/1), the arrival of fusion power (50/1) and finding life on Saturn's moon Titan (10,000/1).
Gravitational waves, tiny ripples in space-time predicted by Einstein, started out at 500/1 to be detected by 2010. But the bookmaker slashed that figure after a rush of bets - some of them from physicists - which made headlines at the time.
"If I remember correctly, we were contacted by a colleague," said Prof Rowan, from the University of Glasgow. "Neither Jim nor I are gamblers, so we had to figure out how to set up an account with Ladbrokes. It took us some time to do that and by then, the odds had started to drop."
Eventually they sank to 6/1 before the book closed, she recalled.
"They stopped taking bets, because our community all went - this is too good to miss! We might see something."
Ligo is an international project set up to detect gravitational waves using two huge laser instruments in the US states of Louisiana and Washington. It was decades in the making and UK scientists, including Prof Hough, were key to its development.
Prof Rowan said there was general agreement that detecting gravitational waves with Ligo's first run, from 2002 to 2010, was "possible but not probable". Many researchers thought they would need to wait for the subsequent upgrade to boost the devices' sensitivity. But there was always a chance.
She remembers 2010, and the chance of £2,500 in winnings, whistling past without much sense of disappointment.
"I can't remember what I was doing, but we all remembered the bet," Prof Rowan said.
In the end, of course, a set of Einstein's fabled waves wobbled through Ligo's laser beams in September 2015, just as the team were turning the instruments back on as "Advanced Ligo" after a major revamp.
These minuscule ripples had travelled across the cosmos, at the speed of light, for 1.3 billion years. Their source was the spectacular merger of two very large black holes.
"It was worth the extra six years," Prof Rowan said.
Dr Fred Raab, head of the Ligo lab in Hanford, Washington, said that detecting a black hole merger, in particular, was something that nobody would have bet on. Most of the team's attention had always been focussed on detecting a pair of neutron stars, merging to form a black hole.
"The reason was that binary neutron stars were known to exist and there was a crude estimate of the number within a certain distance of Earth that might merge within the lifetime of the Universe. Those estimates varied by a factor of a thousand, but were the most solid estimates that existed for any of the possible sources of gravitational waves."
By contrast, merging black holes were an unknown unknown.
"Since there were no known black hole binaries, there were only mathematical simulations that varied between predicting we would see them once per year with Initial Ligo (the experiment before its upgrade), and saying they cannot form at all."
That made September's detection historic on multiple fronts, said Prof Rowan.
"The very thing that we detected was a surprise - two black holes. And they're big; their size is very interesting to astronomers. So it's amazing that immediately we're doing fantastic science.
"We're willing to lose out on the £2,500. This is worth much more."