"(in 6429)" in allkeys.txt

[Per Starbäck]

In the DUCET file allkeys.txt,
http://www.unicode.org/Public/UCA/latest/allkeys.txt ,
there is "(in 6429)" as a comment for some characters.
I first didn't understand why, but then I realized those are control
characters that are part of ISO/EIC 6429.

Why is that pointed out explicitly in that context?

The reason I'm asking is that I was looking at the proposed new version
of this file, and was thinking about suggesting a short note in the
comments in the beginning of the file.