Yes, 30 years is a not a long time, as I have a Randall knife sheath my father treated regular with Neatsfoot oil starting about 1973, and today the leather is coming apart. It never had any Pecards used on it, and no need to bother today as the leather is too far gone. Neatsfoot oil is good for your boots that you probably won't wear over 5 years, but not your prized leather.
The two Randall knives shown below have each had their sheaths treated with a preservative. The top knife was made about 1960 and has had Pecards used on it for the last 30 or so years. The bottom knife was bought for my dad about 1973 and he treated it with Neatsfoot oil.
It is recognized that Neatsfoot oil darkens the leather.