Can you please explain how the casing stones were laid first on G2 when they had to carve sections of the bedrock behind them into courses first?
You are talking about a quite specific section of this pyramid.
The method is the same as for any structure built over an existing mound.
On the Great Pyramid the base line was some distance out from the mound allowing sufficient access to work behind the casing stones.
However, on Kafre the mound was already quarried bedrock in one section, therefore there was no need for any support stones on the northern corners as the first few courses were roughly cut prior to the veneer. The lower courses of Kafre may have been core and mantle due to the fact that the solidity of the mound did not require the more technical integrated masonry found on the upper courses.
Still doesn't mean that the base line wasn't initially established and the casing stones laid first on the bulk of the pyramid. Obviously much easier with the cut platforms. Not so easy higher up though.
Looking at Kafre, I still have doubts, as with Khufu, whether or not, the core courses are correlated with the casing stones in height.
Also, it seems reasonably clear that the layered method was used in lieu of a mound.