Warren in Lancaster, PA
There are more variables to abrasives than just particle size. For instance, emery and tripoli, both historical polishing compounds and strop preparations, break down during use. The effect is that they cut more quickly initially, then break down into smaller and smaller particles as polishing proceeds. They also have more rounded particle shapes than harsh abrasives, so scratches are more shallow. Some sharpening stones have similar properties, allowing much finer polishing than their initial particle size would suggest.

The particle size model for abrasives is one dimensional, and rather clumsy.

It could well be that for the green bar, the Aluminum oxide does the work and the Chromium oxide does the marketing.