Ok thanks again.
Much clearer now from an expert/senior member[!!] and thanks for the tip about using a different email address too! That will be arranged. :-)
Most of my new recruits are data users and are not worried about what phone number they have. So changing phone numbers after one month will not be a problem to them.
However, being a novice [!], I believe giffgaff do not allow phone number swaps between giffgaff accounts, via PAC codes etc, [except on very special circumstances with Agent’s help].
Indeed, I had to do this when I first started with giffgaff as a result of some internal failure. Of course, you can sim swap but that retains the same phone number and does not count as a recruit. :-(*