The original Nikkor-H 28/2.3 has 6 elements in 6 groups. Although a modest lens by modern standards, it was the first successful wide-angle 28mm lens for SLR cameras and helped them to become the general purpose camera system over rangefinder cameras. You can read about it here:
https://imaging.nikon.com/history/story/0012/index.htm.
It was followed by the K (New Nikkor) 28/3.5 which has the same optics with some refinements that allow the close focus limit to be reduced from 0.6m to 0.3m.
In 1977 it was replaced with an all-new AI 28/3.5. The optics are completely revised but remain in a similar 6/6 element layout.
In 1974 Nikon released the slightly faster K (New Nikkor) 28/2.8. This lens focuses to 0.3m without CRC. This lens features a more involved 7/7 element design, but if you look closely the general arrangement of lenses is similar to the original 6/6 design, except the second concave element is replaced by two concave elements:
the K 28/2.8 was upgraded to AI in 1977.
In 1981 the AIS 28/2.8 was introduced, this has an even more sophisticated optical design, now with CRC and focusing to 0.2m. Again, if you look at the optical design, you can see it is really a further development of the AI 28/2.8, except the thick middle element is now split in two with CRC applied across the gap:
The cheaper Series-E 28/2.8 was introduced in late 1979 with a simplified 5/5 optical design. The first AF 28/2.8 (narrow plastic focus ring) and the AF 28/2.8 new (rubber focus ring) have the same optics. These all focus to 0.3m
The AF 28/2.8 D has a new 6/6 element optical design. It focuses to 0.25m without CRC. The arrangement of lens elements is very similar to the original Nikkor-H 28/3.5. Performance is reported to be much better than the older AF designs, probably similar to the AI 28/2.8 but not as good as the AIS version:
