According to the Rigby table in Brown's Book, London Gunmakers, 17250 was 1905, 17,550 was 1910.

1905 would be early for a 470 which was supposed to have been introduced in 1907 by Lang but I'm not sure that's accurate, I've heard it was earlier than 1907.

Is your gun an original 470? it was not unusual for 450 Nitros to be rebored after the India ban. What do the proof marks say?