I’ve verified that with the Materieal LERP function, an Alpha of 0.0 selects the A input, and 1.0 selects the B input. The documentation that comes up when doing a Ctrl+Alt over Lerp states:
If Alpha is 1.0/white, the first input is used. If Alpha is 0.0/black. the second input is used.
This is backwards. The web documentation Math Material Expressions in Unreal Engine | Unreal Engine 5.1 Documentation is correct though. It’s online the in-editor documentation that’s wrong.
I’ve recreated the same project, minus the normal.
I did some experimenting with the clamp and this is what I have come up with. A calls 0.0 and B calls 1.0. However, within the clamp if you leave the minimum zero and set the max to one you are telling the material you have this array of numbers between 0 and 1. You can be any one of those numbers.
While setting only max to 1.0 I got some interesting material coordinates that returned mostly one but with the other two textures being tiled around the edge.
In order for this system you either set both numbers to 1.0 or both numbers to 0.0 to tell the material you can only call this texture at this numerical value.
However, even if this is what you were doing. The values for A are 0.0 and the values for B are 1.0.
Thanks,
Still not fixed 
Hey Dustums,
Apologizes for the confusion. I was able to verify what you are reported and have entered a bug for the issue (UEDOC-2951). We appreciate you bringing this to our attention, and if you have further questions or need additional assistance please let us know.
Cheers,