What to do about left-over .lock files?

I seemed to have two of my four Zope worker processes (client2 and client3) running an old version -- they seem to have survived my last update (where I simply lifted psycopg2 from 2.5.5 to 2.8.6); no .pid files for them were present, just .lock files. (They sometimes complained about not being able to close a closed connection, which should be fixed by psycopg2 v2.7.5).

First thing I did -- I disabled these zombie workers in the (Apache) balancer-manager.

It was not possible to stop them, so I killed them (no -9 or the like) and, as soon as ps -p ... didn't find the process anymore, deleted the .lock files.

After starting the two workers again, I found that only one of the looks like expected (with both .pid and .lock file, and the other one (client3) has a .lock file only again; bin/client3 status still tells me, "daemon manager not running". It seems to work, though, telling from accessing its port via lynx.

What should I do about this?
Ignore the missing .pid file and re-enable that worker?
What is common treatment for such abandoned .lock files?