I apogises in advance for any naivety to this question, but just how is it seemingly ALL locos have ended up at PB? As such I don't decry what they have achieved and continue to provide but do they in fact own all of these ? Are they effectively guardian/trustees/ custodians to all or any of them ?
Most of the people at PB over the past 60 odd years are / were good people. But they all had a taste for almost ruthless "Empire Building". Once anything that could be conceivably made to run on their tracks strayed into their clutches, it was destined to never
They said as much about the Lyell railway carriages. When the Abt railway was being rebuilt and a polite request was made for the carriages to return to their home, PB refused and said words to the effect of "over our dead bodies". Similar things have happened with the loco and rolling stock used during the first attempt at reviving the Walhalla line. When it failed, the rolling stock went to PB and even when Walhalla was successfully revived, the rolling stock that had been used in the first attempt stayed at Puffing Billy and the WGR had to build and scrounge their own rolling stock. There are a couple of other instances of similar behaviour from the PB Empire.
But this dedicated utter ruthlessness in snatching everything they could lay their paws on has resulted in lots more being preserved than if PB had more modest goals and had only taken what they needed. Examples are the huge collection of original VR narrow gauge rolling stock. They hold far more than they could have ever expected to use 50 years ago. They also collected a vast range of other narrow gauge stuff ranging from logging locomotives to a massive semi-streamlined express locomotive from Silverton (which could never run on their track). Most of this stuff would have been scrapped if it wasn't for the efforts of the pioneers of PB.
A few things did escape them, the corpse of the second Powelltown Shay was bought by a private collector who refused to sell it to PB, as a result it has been neglected in private ownership for the past 50 years and is now probably beyond restoration. So instead, they bought a Shay from Taiwan. This Shay is still sitting in a shed, but they look after it, so it's possible that one day it could conceivably restored... but only if PB don't have to relinquish ownership.
So it appears to modern eyes that PB has a very infant like "If I see it, I own it forever" attitude. BUT if it wasn't for the long dead pioneers of that railway having this attitude, an awful lot of priceless stuff would have been scrapped. However it is a shame that the people who now run Puffing Billy still hang onto this approach when some of the stuff they own could be better utilised elsewhere.