I am running Slackware64-current with multilib; slackpkg is pointed at the 'current' mirror and I run update, upgrade-all, install-new (clean-system from time to time).
Originally I installed 14.1, then switched to current and it hasn't changed since.

I encountered a problem when tried to use udiskie (both from SBo & ponce repo): it complained about gi module missing. It is provided by the 'pygobject3' package in current and 14.2 (but not in the 14.1). The problem was I didn't have it and 'slackpkg install-new' would not solve that.

I know that 'install-new' worked as expected previously (e.g. when pulseaudio was added, it installed the new packages alright). My question is why it didn't in this case now? Am I missing something with slackpkg?

Interestingly, CHANGES_AND_HINTS.TXT (for current AND 14.2) doesn't mention the addition of 'l/pygobject3' since 14.1 which is wrong.

have you checked it on /var/log/packages?
probably you have installed it from SBo (from 14.1)