Culverton said that's where Sherlock was, in the hospital. It is also the number on the piece of paper on Mycroft's fridge in The 6 Thatchers. With Sherlock's deduction that his imaginary guest Faith drove a left-handed car, [which we do here in the US] could Euros have spent time, may much time, in a psych ward herself,maybe out of the country sometimes, so long that Sherlock didn't recognize her. Awaiting answers this Sunday....