It emerged on Tuesday that the test, which had been criticised for being too lax in its previous form and was tightened up almost two years ago, had been placed in the hands of the unnamed specialists.
It was also revealed that several investors have fallen foul of the test and Coates, speaking at a House of Commons Select Committee inquiry into football governance, said: "We don't know the numbers but we do understand that there are people that wanted to buy and failed to buy (clubs) because they didn't pass the test."
Coates revealed he was one of the driving forces behind the recruitment of specialist lawyers, saying: "It's something that I wanted them to do. If you want to improve the fit and proper persons test, you want to make sure it's properly vetted and I thought a specialist company would be the best way to do it."
Sunderland chairman Niall Quinn added: "There is an international company who, covertly, will find out everything they need to know about somebody coming into the game.
"We can't tell anybody who it is. It's up to the Premier League to make that public."
Asked why the names of those who had failed the test had not been made public, Quinn said: "We couldn't make that public because people could come along and maybe try to sue us."
Manchester United chief executive David Gill added: "The Premier League has learnt from certain situations. We learnt from the Portsmouth situation and we as a group of clubs supported very wholeheartedly the recommendations from the executive to improve the rules in terms of financial information.
"The vetting of owners, that's been improved."
Meanwhile, all three men backed UEFA's new financial fair play rule - which ostensibly prevent clubs spending more than they earn - claiming they would like to see it eventually adopted by the Premier League.
Source: PA
Source: PA