"worth" can have two meanings in this context. $100 from 1917 can be worth exactly $100 today. Or it can be worth what you can buy with it.

Some folks will see a $100 bill from the era and see an old $100 bill. Some folks will imagine what that $100 took to save back then, and what it bought.

FWIW my brain automatically went with "the goods that can be bought with $100" - such as what I could buy in a grocery store today with $100 would be about what I could buy with $3 back then.

I never considered the other reading until this thread. It was obvious to me the author meant "you can buy 97% less stuff today with the same $100".