In the case of this patient little sufferer, this condition may most likely have been present from birth. When this as a piece of trivia was not well known to others, the particular signs of it served as a distinguishing mark when pretenders claimed to be Alexei Nikolaevich. But as this condition is not really that uncommon among little boys, I think hemophilia and possibly hallux valgus (apologies for spelling) must have been more telling indicators that 'Yes, it is the Tsarevich' or more likely 'No, this is not him.'
Now that this even gets brought up here (which probably would have embarrassed the lad) it cannot unmask pretenders of his generation, which has all passed.
The reason I mention hallux valgus is that I wonder if the picture of him synchronizing his watch with his father during the Great War shows him with it - the same condition Anastasia had.