I do not know if anyone has remarked on this but the stonework in parts of the great pyramid that were not intended to be seen is not that good quality.
I have been told that when buikding with stone you should keep the old bedding plain in its original orientation.Sone of the stones in the core are on their side.

With over three million stones, having a few less than perfect is understandable!
And where did you get the information some were "on the side"? I thought most of the blocks were square--all sides more or less even.

I have been to the pyramids. By on their side I mean with the bedding plain in the wrong direction. As far as I remember there were quite a few like that.
Also many things you read imply that all the blocks are placed so you can not get a sheet of paper between them but as far as I remember in some cases some of the internal stones were packed with bits of rubble.

I don't know about the great pyramid, but from what I have read about the cores of the pyramids of for instance Pepi I, the cores were in some cases even made out of some type of rubble.

In the core of the pyramid of Pepi I for instance they have found stones from a mortuary temple of a queen. So at least some time later in history the cores of the pyramid were not constructed from prime building materials.
I would not be surprised if that same technique was used in the earlier pyramids.

I think that's why they refer to the outside stones as a casing? That layer was made of the nicer Tura Limestone.

During the later period of pyramid building, it was quite common practise for the core of the pyramid to be build of rubble. Even mud-brick was used, which was not a bad process, until the outer layer of limestone was removed for later building projects. The mud-brick soon disintergrated in the wind and rains, leaving a big pile of dirt! Those pyramids that lasted are those that were built of stone throughout.