The first three numbers comprise the logical version number. We use the fourth to disambiguate different builds of a release. So, v14.0.0 and v14.0.1 area planned releases of the product. We may produce a number of release candidates, both internal and external, which are tracked using the fourth digit, like v14.0.0.5 and v14.0.0.7, but we treat both of those as v14.0.0 since they are two builds of the same thing.
We want it to be easy to keep multiple versions of SlickEdit on your machine, if for no other reason than it makes it easier on us to test and support the product.

However, we didn't think it made sense to treat different builds of the same release the same way as different releases.
As previously pointed out, you do have the option of overriding the default install directory if you choose. I hope this helps you to better understand our nomenclature.