. . .In any event, the land grant's basic function is to provide the noble with an income, to keep his family in the lifestyle befitting an Imperial noble. If he does not have the land, how he obtains the equivalent income becomes an issue, (and possibly story idea)
Yes. I was not trying to say that perhaps the noble on the planet didn't have any land grants at all. What I was saying is that perhaps his land grants are somewhere else entirely.
Just as a quick example using the pseudo-real world:
The empire of Ftang extends over much of the known world. The country of Aarl is a part of the Ftang empire. It has only recently become a part of the Empire of Ftang after petitioning the Emperor since the people of Aarl think that as part of the Empire its citizens will benefit immensely from the knowledge and culture of Ftang as well as hoping that it will keep the soldiers of Ftang from burning their cities.
Emperor Wibble thinks that it is important that there be representatives of the Empire in Aarl to remind the people of Aarl of the immense benefits of commerce, mutual defense and non-ignited buildings. He asks one of his nobles, Count Downs to go the Aarl as his Imperial representative. Count Downs is of course the Count of Downs, located in Araq, Viscount of Grind, located in Ahard Plas, and Baron of Rhed, which is located between Araq and Ahard Plas. He holds land grants in all these places as part of his titles and the taxes from these are what he uses to maintain his and his family's lifestyle.
He doesn't, however, own any land in Aarl. When he is in Aarl as the Imperial representative he has no authority of law although as a representative of the Empire and Emperor he does exert a certain amount of influence and some defacto authority. He doesn't even own a house in Aarl and as there is no official embassy of the Empire in Aarl he instead stays with the Duke of Aarl in his castle, who treats Count Downs as an esteemed guest in order to A) try to establish a friendlier relationship with the influential Count, B) save a little money by not having to shell out for a separate building since it has been made clear to him that certain amounts of hospitality are expected (i.e. he's not only got to have Imperial representatives in his Duchy but to remind him of his place he is expected to foot the bill for it) and C) because it lets him keep an eye on the Count just in case other people want to try to convince the Count to send an unfavorable report to the Emperor suggesting that the Duke be replaced.
Incidentally Count Downs is not the only Imperial representative in Aarl. He is simply the ranking member. The knights Sir Prize and Sir Render have also been sent as a lesser representatives. While Count Downs deals with the nobles of Aarl on matters concerning commerce, trade, progress, and most importantly how all those will related to the taxes Aarl is expected to pay to the Empire Sir Prize is suppose to conduct a comprehensive review of Aarl's military preparedness so that the Empire won't be forced to sent troops to help defend the borders of Aarl as well as ensuring Aarl will have a supply of troops to send where the Emperor wants them to go.
Sir Render on the other hand appears to have been sent as part of the Imperial delegation because of a rather embarrassing incident in which he advanced his troops in the opposite direction of the enemy 'in the interests of fortifying the Emperor's defenses' in a recent battle. However, as his father is an influential Duke Sir Render's 'tactical mistake made purely out of the immense love he feels for his Emperor' earned him an all expense paid trip to the edges of the Empire where he is expected to take the opportunity to reflect on his actions.
He is of course actually a spy and his purpose is to establish a spy network in Aarl since the Emperor is a big fan of keeping your friends close and your enemies closer.
So there you have it. Multiple nobles in the land which do not own any land or exert any legal authority there (which is all the 'Noble' column really requires of the nobles it lists). There are other nobles who would not have a place in the 'Noble' box such as the Duke and other various nobles of Aarl. One of the listed nobles does exert some authority even though he doesn't actually have any. A second doesn't really exert any authority at all but is there fulfilling an important role beyond simply glad handing people and a third one appears to be there because he's in sort of a 'time out' (which is something that happened often enough that it allows him to fulfill a different role for the Empire).
This doesn't mean that such nobles would never have land grants or legal authority where they are residing. The Emperor could decide that after the unfortunate and completely accidental death of the Duke of Aarl in which he accidentally tied himself to a chair, fell down two flights of stairs before falling out a window and onto a dagger in the castle moat where he drown that perhaps Count Downs should take over running Aarl (and as he is now responsible for Aarl he also inherits all of the previous Duke's lands).
This is just an example in which we haven't even really come up with anything too contrived (beyond names) where there are multiple noble representatives, none of whom have land or legal authority in the land where they are found.