I ran -stable for 2 or 3 years on my production platforms. At that time, -stable packages were being built and deployed on the project's mirrors. I moved to -current around 3.8 or 3.9. I'd had a bug requiring active cooperation with a developer. Once the problem was resolved, I stayed -current on production.
Some time after my transition, the project ceased backporting -stable ports or building -stable packages, due to the workload required. Things stayed that way for several years; it is a small project with limited resources.
---
As I've stated above, "make update" is the wrong target. You may find make package (or make repackage) followed by make update will be more effective than a make update alone. The latter does not build ports, it is a package installation directive only, as is FORCE_UPDATE, per bsd.port.mk(5):
Code:
update Update an existing installation to a newer package: scan
the installation for a package with the same FULLPKGPATH,
and update it using `pkg_add -r' if a newer package is
available. In multi-packages ports, all relevant packages
are updated. See UPDATE_COOKIES_DIR and FORCE_UPDATE as
well.