PkgBase: Can not upgrade base system

For a client I tried PkgBase and followed the procedures recommended (first
build the OS from /usr/src/, installworld/kernel, then proceed with pkg update
-r FreeBSD-base and pkg install -g 'FreeBSD-*'.

This doesn't work for any update I try to apply. Since the target host is a two
years old Intel NUC based on some Broadwell snail CPU, building world and
kernel is performed on another, much more potent host.

In the first place, when performing a "pkg upgrade", the system complains about
mismatching OSVERSION, 1200055 forthe running system, and 1200056 for the
packages to be updated. When setting env OSVERSION=1200056, pkg (not
pkg-static!) complains about revision numbers (the long date trailing the
package's name), for instance the newest one is 

FreeBSD-hast-12.0.s20180123050738.txz

contained within the repository to be used for the update, but installed is
something older, like FreeBSD-hast-12.0.s20171103114456.txz.

When trying pkg-static, I get a crash of pkg-static, segmentation fault is its
death-cause.

How am I supposed to update a base system via PkgBase?

Kind regards,

oh

p.s. sorry for the lack of data, the box in question is on a remote site
without net.