I own vapcaps sporting the second generation tip and the third generation tip; the first tip to be manufactured in-house at Dynavap.
The third generation tip was released last fall and it improved the air flow and convection ratio with the addition of more grooves on the outside of the tip. This allowed more air to be pulled and heated between the cap and the tip.
The forth generation and current tip has improved upon this feature even more by creating deeper and wider air channels.
I don't own a forth generation tip but am hoping to buy a few during the 420 sale.
I believe that the earlier tips had fewer and thicker heat disbursement fins as well.
Unfortunately, I don't have direct knowledge of all the refinements that took place in the Vapcap evolution. Maybe someone else with the earlier models can add to this.