I'm not so convinced about it being admin only - they have separate laws on how to react if an outside agent gets involved in the match vs. if a sub or team official gets involved.Maybe we could add this to example #97 of how the new LOTG clearly weren't proofread before release?
Or perhaps the clause noted above is simply inapplicable when there is no team list (which doesn't cause any problems in interpreting that clause).
I actually find it strange that IFAB have chosen to include in the LOTG what is essentially an administrative concern.
With that in mind, it then becomes their responsibility to define what an outside agent is. And as the OP has pointed out, they've failed to clearly do that in competitions where the referee hasn't been given a team sheet, or in competitions where the team sheet doesn't need to include an exhaustive list of every possible coach/physio/team official.
As you say, common sense will tell you pretty quickly who is involved with the team and who is just spectating, particularly at low level football - but the laws should exist so that we don't have to apply common sense in that way.