It's from the last rule that was applied - basically, the rules specify transitions, and the last transition was into CAT in September 2017.

On Mon, 28 Jun 2021 at 15:55, vaibhav shrivastava <vaibhav.sh17@gmail.com> wrote:
Sorry one more question.

# Rule	NAME	FROM	TO	-	IN	ON	AT	SAVE	LETTER/S
# Vanguard section, for zic and other parsers that support negative DST.
Rule	Namibia	1994	only	-	Mar	21	0:00	-1:00	WAT
Rule	Namibia	1994	2017	-	Sep	Sun>=1	2:00	0	CAT
Rule	Namibia	1995	2017	-	Apr	Sun>=1	2:00	-1:00	WAT

How I decide to use CAT as 

2:00	Namibia	%s
if I check the current year 2021 and %s seems to pick value from where? These rules are till 2017, so from which line does %s pick CAT.?

On Mon, Jun 28, 2021 at 8:12 PM Jon Skeet <skeet@pobox.com> wrote:
On Mon, 28 Jun 2021 at 15:39, vaibhav shrivastava <vaibhav.sh17@gmail.com> wrote:
In April sun>=1 does it change to WAT?

Not after 2017, no - because the rules only go as far as 2017. 




-- 
Regards,
Vaibhav