Grade Master3 cartridge--Moving Iron Design

Pickering is listed in the legend to your figure after point #2, as an example of "moving magnet". As I am sure you know, Pickering and Stanton were associated with each other. Most models of Pickering have a corresponding model among Stanton cartridges.  Both companies marketed a low output MM, the Stanton 980LZS (also the 981 variant) and the Pickering XVS7500. These have a much lower inductance and internal R than do the typical high output MMs from anywhere. It IS interesting so see illustrated the differences among MI, variable reluctance, and induced magnet (IM) types.  We usually don't bother to make a distinction among types 3, 4, and 5. For example, in this thread several refer to Decca as MI.

The drawing of the Decca/London pickup design on the new London site looks very similar to the drawing of the moving iron design in the Gramophone article. It’s the one in the upper right hand corner of fig. 2. The inclusion by the article’s author of the Decca in the variable reluctance category does not align with the description and drawing (bottom right corner) of a vr pickup in the article.

Variable reluctance refers to an operating principle, not a specific mechanical design. Here's a simple explanation -

Coils coupled to each of the magnetic circuits pick up flux changes which occur as a result of armature movement causing flux changes in the common gap.