The F-5 evolved from the T-38. The F-20 Tigershark was the next generation. The F-16 was chosen by the USAF instead. Only 3 were ever produced.
Iran actually developed and currently flies a newer version.
I have not kept up with the technical details of the various incarnations of the F5 and it’s descendants.
I have noticed each new generation of the aircraft etc. ever since I was a kid and Daddy worked at Eglin. I noticed the F5 and trainer versions and kept seeing it being developed in other newer models. I knew there was a direct lineage to the new Super Hornet.
The F-5 came first. It started the line that ended with the F/A-18.