Pedant ON
An instruction can only be given - and is only meaningful - when you are under some form of "Control".
"Remain outside controlled airspace" is an instruction.
If you are in Class G, waiting to enter Class D, there is NO Air Traffic "Control".
Ergo, the phrase is unnecessary - indeed, in law it could be said to be ultra vires ...
Pedant OFF
True, in which case maybe we should be asking the pilot to confirm he will be remaining outside ... which is a request for information, not an instruction. That said, how can I instruct you to join if you are in Class G as I can't give you any Air Traffic Control instructions by your reckoning ??
Alternatively, ATC say nothing, let the infringement occur and leave it to the magistrates court to deal with, no doubt with the CAA eventually becoming sick of GA and putting in some draconian rules which will hurt all GA pilots.