Question about Logstash plugin pack scope?

I have installed Logstash onto a staging server and am using the bin/plugin pack command to create an archive of installed plugins for installation on a non-Internet connected production server.

The command works fine - but the created archive does not contain my custom plugins, both of which installed successfully into Logstash on the staging server.

I can also see my custom plugins when I execute bin/plugin list.

So - is there any way I can include my custom plugins in the archive generated by the pack command ?