[tz] Wisconsin daylight savings 1957

[Paul Eggert]

On 4/16/21 7:39 PM, TJ via tz wrote:
> In the tz db for North America, it looks like Wisconsin is using
> America/Chicago which has a few rules for the time period in question:
> Rule	Chicago	1922	1954	-	Sep	lastSun	2:00	0	S
> Rule	Chicago	1955	1966	-	Oct	lastSun	2:00	0	S
> 
> It appears to me that Wisconsin might need some modification?

If the affected timestamps all predate 1970, we should be OK as far as 
tzdb is concerned, as Wisconsin would still agree with America/Chicago 
for timestamps after 1970.

Shanks divides Wisconsin into six distinct regions depending timestamp 
histories before 1970. I expect that none of these histories agree with 
Chicago's (and I also expect that Shanks' divisions are not completely 
accurate, and that there may be more than six regions). Surely this 
would be 'backzone' file material at best, though.