Here it's the documentation of the plugin when you load it inside your openfx host.
So this is not for the "builder" but for the end user. If its CTL file is not recognized, it will need to know the real version of CTL used to build the plugin.

In few month, maybe someone will built the plugin with CTL 1.6. So it's not a good idea to put hardcoded version, because it's not reliable...