While others are correct that the "floating" address pin on a larger than required device doesn't need to be tied... I'd highly recommend it.
Some devices may lock up if the address pin is oscillating (the spec sheet would show how an address setup/hold time can be violated)
Worse is the possibility that the oscillation generates spurious RF which could interfere with radios/cellphones/etc.
These behaviors aren't probably too likely, but are pretty challenging to troubleshoot.... Easier to tie the pin... Ground/VCC or the highest address pin are all good possibilities (designs I've been involved with all tied pins to ground since it pulls slightly less current)
Keep in mind this advice comes from my experience in embedded hardware/software... But not for pinball's.
PS. Thanks for all of the great resources here for a pinball newbie!