don't take me wrong, i guess we all do ils captures out at 30 or more miles. it works and even well. but it won't stand in front of a court if comes to that. i'd take the ils at 75 miles if i had only that to find a field. the certification procedure is based on rates of occurence of failures. out to 25 miles the failure rate is acceptable (for the government, the insurances, ...). up to 20000 ft the rate of occurence of a flight destabilisation is acceptable (for the same people).
again if flying at 22000 ft and absolutely (for what reason i don't know ...) needed to set some flaps then i wouldn't hesitate (knowing that my flight envelope is not demonstrated to the same reliability).
the original q was about a safe capture of loc & glide signals.
as certified it's safe to 25 nm.
seb