This blog is updated daily.
A general description is here.
Where time zones have changed abbreviations over the years, the software tries to more consistently use the abbreviation appopriate to the time or if that is unknown, the current abbreviation. On some platforms where the C function ‘localtime’ changed the ‘tzname’ variables the reported abbreviation could have been that of the last time converted.
‘available.packages()’ is better protected against corrupt metadata files. (A recurring problem with Debian package ‘shogun-r’: PR#14713.)