Guinness World Records says it does not recognise claims that a 100-year-old Briton is the world's oldest marathon runner.
Guinness World Records says it has not ratified the record as Mr Singh cannot show a birth certificate from 1911.
His trainer, Harmander Singh, says such documents were not made in India then.
Fauja Singh is said to hold a number of world records, but the BBC's 5 live Investigates programme has learned that none of these records has been ratified by Guinness World Records.
His British passport, showing his date of birth as being 1 April 1911, as well as a letter from the Queen congratulating Mr Singh on his 100th birthday, have been shown to the organisation. But it says these are not considered sufficient proof of age.
A letter from Indian government officials stating that no birth records were kept in 1911, and a statement from a former neighbour in India, have also been passed to Guinness World Records, but the organisation says these too are not evidence enough.
Fauja Singh recently completed the Toronto Waterfront Marathon in eight hours, 25 minutes and 16 seconds, finishing in 3,850th place, ahead of five other competitors.
He received worldwide publicity celebrating his position as the oldest man to complete a marathon - numerous media organisations, including the BBC, announced he had made it into Guinness World Records.
It has also been widely reported that Mr Singh already had a place in Guinness World Records for the over-90 marathon category after running the 2003 Toronto marathon in five hours and 40 minutes.
But Guinness World Records has in fact not ratified this record, although Mr Singh is listed as a record holder for this performance on the World Masters Athletics website - an organisation which accepts a passport as a proof-of-age document.
Speaking to the BBC, the editor-in-chief of Guinness World Records, Craig Glenday, said: "We would love to give him the record. We'd love to say this is a true Guinness World Record, but the problem is there is just no evidence.
"We can only accept official birth documents created in the year of the birth. Anything else is really not very useful to us."
It is also claimed that Mr Singh holds UK records for the 200m, 400m, 800m, mile and 3,000m for his age group, but British Masters Athletics (BMA) says these records were not official as the event where Mr Singh performed was not attended by official timekeepers, as well as the fact no proof of Mr Singh's age was provided.
His name does not appear on the BMA website's list of record holders.
However, Fauja Singh recently claimed another eight records for 100-year-old men by completing eight distances ranging from 100m to 5,000m and it looks like those performances will be recognised by the British and World Masters Athletics. The Canadian official who oversaw his performance says Mr Singh's British passport was shown and is considered valid proof of age.
Mr Singh, who worked as a farmer in the Punjab before moving to Britain in 1992, does not speak English, and so his trainer has responded to the allegations on his behalf.
In the past, Mr Singh has appeared in advertisements for sportswear firm Adidas, for its "Nothing is Impossible" campaign.
His trainer, Harmandar Singh, says he thinks recognition by Guinness World Records is important: "I think it's important to everybody who's over a certain age, because it inspires them and allows them to think 'yes, it is possible'.
"However, the fact remains that the Guinness Book of Records has its rules, and I think they are quite right to have them.
"However, in the developing countries, their standards simply aren't up to western standards."