Upstream changelog contents (only the data-related aspects of this apply):
Release notes are:
> Briefly:
> Revised predictions for Morocco's changes starting in 2023.
> Canada's Yukon changes to -07 on 2020-11-01, not 2020-03-08.
> Macquarie Island has stayed in sync with Tasmania since 2011.
> Casey, Antarctica is at +08 in winter and +11 in summer.
> zic no longer supports -y, nor the TYPE field of Rules.
>
> Changes to future timestamps
>
> Morocco's spring-forward after Ramadan is now predicted to occur
> no sooner than two days after Ramadan, instead of one day.
> (Thanks to Milamber.) The first altered prediction is for 2023,
> now predicted to spring-forward on April 30 instead of April 23.
>
> Changes to past and future timestamps
>
> Casey Station, Antarctica has been using +08 in winter and +11 in
> summer since 2018. The most recent transition from +08 to +11 was
> 2020-10-04 00:01. Also, Macquarie Island has been staying in
> sync with Tasmania since 2011. (Thanks to Steffen Thorsen.)
>
> Changes to past and future time zone abbreviations and DST flags
>
> Canada's Yukon, represented by America/Whitehorse and
> America/Dawson, changes its time zone rules from -08/-07 to
> permanent -07 on 2020-11-01, not on 2020-03-08 as 2020a had it.
> This change affects only the time zone abbreviation (MST vs PDT)
> and daylight saving flag for the period between the two dates.
> (Thanks to Andrew G. Smith.)
>
> Changes to past timestamps
>
> Correct several transitions for Hungary for 1918/1983.
> For example, the 1983-09-25 fall-back was at 01:00, not 03:00.
> (Thanks to Géza Nyáry.) Also, the 1890 transition to standard
> time was on 11-01, not 10-01 (thanks to Michael Deckers).
>
> The 1891 French transition was on March 16, not March 15. The
> 1911-03-11 French transition was at midnight, not a minute later.
> Monaco's transitions were on 1892-06-01 and 1911-03-29, not
> 1891-03-15 and 1911-03-11. (Thanks to Michael Deckers.)
>
> Changes to code
>
> Support for zic's long-obsolete '-y YEARISTYPE' option has been
> removed and, with it, so has support for the TYPE field in Rule
> lines, which is now reserved for compatibility with earlier zic.
> These features were previously deprecated in release 2015f.
> (Thanks to Tim Parenti.)
>
> zic now defaults to '-b slim' instead of to '-b fat'.
>
> zic's new '-l -' and '-p -' options uninstall any existing
> localtime and posixrules files, respectively.
>
> The undocumented and ineffective tzsetwall function has been
> removed.
>
> Changes to build procedure
>
> The Makefile now defaults POSIXRULES to '-', so the posixrules
> feature (obsolete as of 2019b) is no longer installed by default.
>
> Changes to documentation and commentary
>
> The long-obsolete files pacificnew, systemv, and yearistype.sh have
> been removed from the distribution. (Thanks to Tim Parenti.)