D-76 has been D-76 since the 1920s. There was no change. Kodak has changed Tri-X many times, generally improving it in subtle ways. It should be noted that for the past many years there have been two, quite different Tri-X films. The first is what is now known as 400TX, available in rolls and 35 mm. This film has a straight-line curve. The other film was called Tri-X Professional and is now known as 320-Tri-X. This film has a pronounced toe, and is recommended for controlled lighting conditions. The earliest record I have for a film called Kodak Tri-X comes from the late 1940s. That was a sheet film with a speed of ASA 160 (old system, near 400 in the current system). In the mid-1950s a new Tri-X became available in 35mm and rolls. It had an ANSI speed of 400 (current system) and was pretty grainy. It could be pushed reliably to 800. This is the precursor of the current 400TX, and had many of the same characteristics. Kodak has made changes to this film about every two or three years. Grain has been reduced until now it is very fine, and there have been subtle improvements to latitude and gradations.