Volume Two, Or Supplemental Volume?

In April 2021 I published a book of philosophies and concepts for our karate system, in particular the older version of this system, which I teach.

I am approaching the point of publication for the next volume.

The first book was 586 pages long.

The one I am working on now has reached 290 pages, and will likely not see much more than perhaps 350 pages.

At approximately half the size of the first book, is it feasible to title it Volume Two, or is this more a "supplemental volume", not necessarily Volume Two?

Traditionally, does a "Volume Two" normally match "Volume One" in number of pages (a few more or less)?

There may not be a third volume, as I think I finally covered just about everything I want to preserve about the old style. These are not "how-to" books, but more "who, what, where, when, and why" books...