- The photos taken by the organisers, or someone posting on their behalf, aren't tagged;
- There were several events on that weekend titled "Jingle Bells";
- Flickr's advanced search lacks useful features like "discard any photos by user X from these search results" or "discard any photos with tag X from these search results" (the latter is achievable by redoing the search, but really, it should be dynamic)
updated to add: according to the EXIF tagging on the photostream, this is about 18:40 into the race, which would put me 40 seconds from the finish line. Which means I was probably still puffing like a steam train and attempting to persuade myself not to back off.