Moore has raised more than 29 million pounds ($36 million) for the National Health Service by completing laps of his garden with the help of a walking frame.
People tuned in from across the globe to watch his progress online, turning Moore into an unexpected focal point for a flood of donations to the state-funded healthcare system which is handling the deadly coronavirus outbreak.
Since completing his 100 laps - breaking both his initial 1,000 pound target and then the Guinness world record for a charity walk - Moore has received over 125,000 birthday cards.
"It's the most amazing outpouring of love for a great man," said James Hodgson, headmaster of the nearby Bedford School in central England, which has taken on the mammoth task of opening and displaying the cards.
The floor of the school hall has been transformed into a sea of goodwill messages, carefully curated by volunteers who have spent hours reading them over the last week.
Even as more arrive every day, Hodgson said the plan was to display as many as possible and send Moore a photograph of the results.