Could be, Eddie. I cannot get to my books now, as the library is undergoing renovation [badly needed] but I think GD Alexander mentioned have to go to work- his lecture tours, to make money.
Those Blue Plaques, BTW, cost a lot of money to have put up. One needs supporters to petition the council, especially on historic houses, and sponsors to put up the money. I doubt Xenia would raise enough interest, especially for such a short stay. Even her grace & favour would be an act of "defacing Royal Property" so would need special effort to mark that place.