[tz] UTC calculation for March 12, 3001 [IANA #1143241], [PR 9419866]

[Lasher, Beth]

In the year 3001, Daylight Savings time is applied on Sunday March 9, 3001 as expected.  (Eastern Standard time).  BUT on the following Thursday, March 12, 3001 at 3 am, it seems that another Daylight Savings Time change is applied.  After March 12, 3001, the UTC time zone offset for Eastern Daylight Savings Time is 3 hours (not 4) and remains that way until the year 9999.  Is this correct?  What is the cause of this second time offset change?