Zorin OS has released editions numerically that follow to higher numbers throughout.
However... early on, ZorinGroup released a "Limited Edition '09" and in the following years, another special edition was released.
That threw the numerical scheme off by Two Editions, so when ZorinGroup started development on Zorin OS 15, they decided to reset the count to the actual number of editions, rather than having the many numerical editions plus two special editions.
This added "two" to the count, bumping Zorin OS 13 up to Zorin OS 15.
Point releases, like Zorin OS 12.4 or 16.1 are Major Upgrade releases that happen Within the same LTS Base Build.
Full releases are editions which have a newer LTS base build. For example Zorin OS 15 is based on Ubuntu 18.04. Zorin OS 16 is based on Ubuntu 20.04.
To the best of my knowledge, numerology and a fear of the number thirteen were not involved in the above decisions.
Wait, what happened to Zorin 13 & 14?
As the previous stable release of Zorin OS was version 12 you might be wondering where versions 13 and 14 went.
Well, don’t panic: you didn’t miss them. Zorin’s lead developer explains why there’s a small ‘jump’ in version number for this release:
“The reason is that this is actually the 15 version of Zorin OS. In between Zorin OS 1.0 and 2.0 way back in 2009, we released a version called “Limited Edition ’09” [so] we decided to take the opportunity to correct the version number with this release.”
The reason I brought it up is because I noticed that number skip and I have a fascination with people and certain numbers. Matter of fact, in NYC, some apartments skip the number 13, naming it 12A instead. Some buildings don't have a 13th floor.
I'm glad that it got nothing to do with that, but a small part of me wished it was so.
In most cases, this has far less to do with the designer being superstitious as much as their preference to meet the demands of patrons and customers that may be superstitious.
While the psychology behind it can be fascinating, its effects can be devastating. Look at the Aye Aye.
Or witch-burning. Which still exists today - also as a form of "Necklacing": in which a tire is placed around a bound persons neck, filled with flammable fluid, then set alight.
I admit, there is no part of me that ever wishes for it to be so.