Watch the Why No Shape 4 or Shape 7? online guitar lesson by Rob Garland from Melodic Soloing: Major Scale
Hang on, why is there no Shape 4 or Shape 7? Good question!
If you start one fret above Shape 3 and play through the major scale (from F to F), you could call this Shape 4 but it is so close to Shape 3 you are covering the same notes.
Likewise, if you start one fret below Shape 1 and play through the major scale (From B to B) you could call this Shape 7, but again it is not worth thinking of this as a new shape because you're covering the same notes. By using just 5 shapes, we can line these shapes up with the pentatonic scale and CAGED chord shapes.
However, if you have studied the major scale modes and would like to also relate them to the major scale shapes, you have the five covered in this course and can easily add shapes 4 and 7 (Lydian and Locrian) which gives you the seven modal shapes.