Right after your question archived (I think it's set for 7 days on WP:RDMA) the Daily Telegraph reader opened a new section with their answer.  I added links to each section pointing to the other, and also added a link to your user page in the new section in an effort to call it to your attention (as I think such an action was supposed to generate a notification).  The new section just archived, so I updated the link to it from the old section, and at the same time noticed that you hadn't chimed in, prompting my note.
There is some discussion in new section about whether, under any calendar, two consecutive Feb 29 full moons would ever occur exactly 823 years apart, but whatever the spread, the average number will be close enough to 823 years that it seems very likely to be the source of the story you read.  ToE