Thanks for the detailed reply.
Yes your assumptions on the terminology is correct. I will use these in future correspondence as it makes it easier when every is on the same page.
Having the image ID written somewhere where Terraform can read it, is the type of idea I was looking for (and makes sense now). I should be able to write the name of the VM/template into a file. Within Terraform use null data source file, read that value (as a pseudo variable) to pass to the vphere-virtual-machine.name. That should allow the TF to find the correct VM and continue. [off the top of the head but, will have to play with that approach to see where I get].
tx