The differences are really only important to collectors. New gen Pmags are probably objectively better than the older ones.
The very first Pmags have slightly different markings and a different floorplate (which has become knowns as the camel toe!) and seem to be the most collected.
Gen 1.5 came with an updated floorplate and updated verbiage.
Gen2 had a new pattern on the mad and older Gen2 will have the dust cover included, were sold in multiple colors and used the white back sealed bag.
Later Gen2 still had the dust cover, were sold in multiple colors and started to come in the brown back sealed bag.
Current Gen2 do not have the dust cover and are currently only available in black.
Gen3 have an updated slimmer floorplate, dust cover, new pattern on the mag with the dot matrix portion towards the bottom and come in black and MCT.
Aside from this, there are tons of other varieties of Pmags that were made. Different non-standard colors, markings, packaging, configurations etc... some more collected and sought after than others.