They were almost positively rebuilt after the pyramid was built. remember too, that they needed to keep production at the Turah Mines steady for half a century in order to build G1 and G2. They almost certainly would have had a large number of blocks strung out as the causeway and as things were wrapping up they "harvested" these stones from the valley port to the Great Saw Palace and then turned the causeway ramp into a covered walkway. It's even possible it was covered during construction.
They needed to have a very large number of casing stones because there was no better place to store them. It's just this simple. I believe there were also a lot of stones in the mehet weret and the ssm.t. They started installing then on the first step of the pyramid near the SE corner by about the third year of construction. From this point they could clad any isolated area that was out of the way of stone movement.
There are simple common sense processes that necessarily apply to all enormous tasks. The Turah Mines couldn't produce 100,000 tons of cladding stones in the 27th year of Khufu's 20 year reign and a million Merer's couldn't have gotten them across the river. Reality trumps everything and every idea. Orthodox beliefs about construction are ridiculous even without the extensive evidence stones were pulled straight up the sides and a lot of material mustta come up the "holy walkway".