Mo Farah would have had to have missed his doorbell ringing several times when he missed a drug test in 2011, a UK Anti-Doping representative has said.
Farah's agent Ricky Simms submitted video evidence to UKAD to back up the athlete's defence that he did not hear the doorbell for his second missed test in the build-up to the 2012 Olympics, where he won two gold medals.
UKAD's Graham Arthur told BBC Radio 5 Live's Sportsweek programme: "For an hour slot test the process is that the drug tester will turn up at the address he or she has been given, ring the bell or knock on the door and try to get the athlete's attention.
"If there's no response UKAD has detailed protocol that involves the doping control officer waiting for a period of 15 minutes, trying the bell or the knocker again, doing the same thing again after half an hour, then 45 minutes and then when the hour is up, the doping control officer completes his or her paperwork and then leaves the address.
"The athlete is advised by UKAD of the apparent missed test a few days later."
Farah's missed tests have come into the spotlight after allegations emerged against his coach Alberto Salazar and training partner Galen Rupp.
Sprinter Mark Lewis-Francis, who himself missed two tests in 2007, backed the 32-year-old and said: "Mo's a great guy, he's a great athlete, he's done the country proud".
Lewis-Francis said his first missed test was down to the doorbell in his new rented flat not working - adding that he took and passed a test the next day - while the second came when he forgot to inform UKAD of a change to his travel plans
"I take total blame for both of them," he said on Sportsweek. "You're responsible for making sure you're available in your slot times.
"Everybody makes mistakes but when you're on two, you've got to sort yourself out because obviously I didn't want to get a ban. I had to be on point with my whereabouts and my hour slots."