Release note documentation does not seem to have x.7 releases of any previous major release in it.
Sonoma notes end on 14.6 and older versions at x.5 - while last public release versions are 11.7.10, 12.7.6 and 13.7.7.
While it looks obscure, it is not exactly new thing...
 
					
				That "Apple security releases" page link is usually always included - while page never includes any betas or RC's.
It looks like 15.7 might be out in September as many have predicted and Tahoe release will come out at (about) same time....