After the title reunification in C22:2005-07, the scheduling started to improve slowly, but for a number of cycles the chess world was faced with overlapping cycles where a new cycle started before the previous cycle had finished. For example, the 2009 World Cup at Khanty-Mansiysk (C24) was played before the 2010 Anand - Topalov title match of the previous cycle (C23).
When I started this blog in 2007, I was never sure how long a cycle was going to last. When a new cycle started I used a question mark ('?') to indicate the end of a cycle, e.g. C25:2011-?. When a cycle finished, I could eliminate the '?', but after Blogger.com changed its interface a few years ago, I wasn't sure how to do this without changing each post separately. Fortunately, a technique for a global change exists and I used it to close the most recent cycles, e.g. C25:2011-13.
Now that FIDE has brought the World Championship into a steady two year cycle, we can predict when a cycle will end, making the question mark unnecessary. I eliminated it for the current cycle C27:2015-16, and hope that FIDE will be able to maintain a two-year rhythm. World class chess needs the stability.
[Reference: A post on Google.com, I have a question about my labels..., explains the technique for making a global change to labels.]