Yeah, you are getting the correct number. It's actually 1451. When I said 1461 above, I was basically falling for my own overly convoluted nonsense and was mistaken. The symbols for the numerals 5 and 6 were transposed on that poster. Again, I suspect there was some obscure in-lore reason behind that, but at this point I just don't know for sure anymore. If that was the case, I definitely wouldn't make that same design decision if I was making the game today. That puzzle already has enough steps to it even without the weird red herrings and inconsistencies.