What are some interventions before 1920 that improved human well-being 100 years later?

More broadly, living conditions have on average improved enormously since 1920. (And depending on your view on population ethics, you might also think that total human well-being increased by a lot because the world population quadrupled since then.)

This effect is so broad and pervasive that lots of actions by many people in 1920 must have contributed to this, though of course there were some with an outsized effect such as perhaps the invention of the Haber-Bosch process; work by John Snow, Louis Pasteurs, Robert Koch, and others establishing the germ theory of disease; or Florence Nightingale pioneering the use of statistics in healthcare.

One classic example is Benjamin Franklin, who upon his death in 1790

invested £1000 (about $135,000 in today’s money) each for the cities of Boston and Philadelphia: three-quarters of the funds would be paid out after one hundred years, and the remainder after two hundred years. By 1990, when the final funds were distributed, the donation had grown to almost $5 million for Boston and $2.3 million for Philadelphia.

(From What We Owe The Future, p. 24. See notes (1.34) and (1.35) on the WWOTF website here for references. Franklin's bequest is well-known but popular accounts are often slightly off in their details.)

Here's an NYT article from 1990 about the fight over the allocation of the funds after they had grown for 200 years.

I'm not sure what was done ultimately done with them, but according to Wikipedia Boston used it to establish and fund a trade school (I think at both the 100- and 200-year marks), the Benjamin Franklin Institute of Technology. 

The rabies vaccine was another one that was developed in 1885 and improved human-well being for rabies diseases.

This is a bit of an amorphous question with tons of possible answers in some sense—e.g., the development of the scientific method—but actually identifying counterfactual benefits is tricky. The examples you listed probably don’t have major counterfactual benefits long into the future.