Of course, Zed! There are lists of definitions for ken, and I doubt anyone would suggest that there is a single definition for the word, period--as is true of many words we talk about here.

But I don't think it would be correct--not that you are doing this--to suggest that we cannot use 'ken' to mean 'knowledge' [or specifically 'range of knowledge'] when we can do so correctly.

Here's the brief MW on this topic:

Main Entry: 2ken
Function: noun
Date: 1590
1 a : the range of vision b : SIGHT, VIEW <'tis double death to drown in ken of shore -- Shakespeare>
2 : the range of perception, understanding, or knowledge <abstract words that are beyond the ken of young children -- Lois M. Rettie>