Having informed England coach Fabio Capello he was not due to see his specialist until May 29 after suffering ligament damage during Manchester City's Premier League defeat to Tottenham last week, Barry then got back in touch to say the actual date is May 24.
The timings are crucial.
The first date is 24 hours before England's final friendly against Japan in Graz and would leave little time for Barry to get fit before Capello's men leave for their World Cup quest on June 2.
But if he is given the all-clear on the revised date, Barry can link up with his team-mates on May 26, when they head back out to their Irdning training camp, with an excellent chance of making Capello's final 23-man party.
With fresh information, it is little wonder Capello completed a volte-face on his downbeat assessment of Barry's fitness 24 hours earlier, which gave rise to speculation Owen Hargreaves was about to receive a shock call-up.
"I know," said Capello, when reminded of Monday's statement.
"But he told me he would be checked by the medics on 29th or 30th of May. Now he tells me it's the 24th. That's six days. It's different. For this reason, I decided to select him."
Yet Capello admits he has no real idea whether Barry will make it.
The 29-year-old certainly sustained damage far worse than City boss Roberto Mancini thought at the time.
However, armed with fresh information, Capello took further advice from England doctor Ian Beasley and trusted assistant Franco Baldini, he decided to take a chance.
"We will wait until the next check before making the decision," he said.
"We don't know what chance Gareth Barry has of being fit but we have time to decide."
FIFA's complicated rules on injured players mean although Barry cannot be replaced in Capello's 30-man squad, if he kept his place for the final 23, which must be handed in on June 1, he could still withdraw through an injury that had been verified, and that replacement would not have to be drawn from the men England submitted today.
Not that Capello wants Barry to miss out.
After being involved in eight of the 10 qualifiers, and having struck up an excellent central midfield partnership with Frank Lampard, Capello is eager to have Barry available for the Group C opener against the United States in Rustenburg on June 12.
"Our doctor spoke with the Manchester City doctor. That was one of the important things," revealed Capello.
"If it is more or less okay on May 24 we have three weeks before the first game.
"Hopefully then he will be ready to start a game."