To be fair, software development in 1954 is not software development today. It's less pure research. It's more akin to building the electrical infrastructure you need for a business. Even though I see the logic of treating software developed as a capitalized asset, I don't necessarily think the outcome will be net good.
"Extend" is a bit of a misnomer because there was no expiration date. Rather, the The Tax Cuts and Jobs Act of 2017 made a change, effective 2022.