A related outside-view argument for the HoH being more likely to occur in earlier centuries:
New things must happen more frequently in earlier centuries because over time, we will run out of new things to do.
HoH will probably occur due to some significant thing (or things) happening.
HoH must coincide with the first occurrence of this thing, because later occurrences of the same thing or similar things cannot be more important.
If we accept these premises, this justifies using a diminishing prior like Laplace.
A related outside-view argument for the HoH being more likely to occur in earlier centuries:
New things must happen more frequently in earlier centuries because over time, we will run out of new things to do.
HoH will probably occur due to some significant thing (or things) happening.
HoH must coincide with the first occurrence of this thing, because later occurrences of the same thing or similar things cannot be more important.
If we accept these premises, this justifies using a diminishing prior like Laplace.