In a comment to Question 29 (the one about The Wealth of Nations) I came to the conclusion that arguably, no leeway was really necessary on that occasion. But I can't say the same for this one.
I know of no reason why anyone in the UK can be expected to remember that The Star–Spangled Banner was adopted as the US national anthem in 1931.
Herbert Hoover was the President who signed the congressional resolution under which the anthem was officially adopted, and the two years' leeway allowed for this answer exactly encompasses his incumbency. Did the question setter know of some reason why we should know it was him?
The only thing about The Star–Spangled Banner that I could have given anything like a date for (before I heard the answer to this question) was the date the original poem was written. I probably would have gone for a year in the War of Independence (1775-1783), but in fact it was during the War of 1812 (actually in 1814).
I haven't been able to find a date for when the poem was set to music. Apparently the tune was composed around 1773, but this is 40 years before the words were written.
In conclusion: I would suggest that the best estimate anyone could be expected to come up with for the date in question is that it was some time between the two World Wars of the 20th century. Even this would call for more generous leeway than two years either way. But I think people are far more likely to guess a date between 1775 and 1783, or (with more justification) some time not too long after 1812. And that, to my mind, makes this a trick question.
© Macclesfield Quiz League 2020