While the graphs I highlight don't show it, the broader paper uses both actual launch data AND experimental data to derive the regression. This experimental data presumably should be available regardless of if this reasoning had been used earlier on launch data. This is one good reason why experimental data is so critical, as real world data can be biased.

You're absolutely right though about this being "Monday morning quarterbacking" with any analysis after the events. That said, two things are clear:

1. The most knowledgeable engineers were strongly against launch (see Ebeling and Boisjoly at Morton Thiokol)

2. There were huge statistical flaws made by decision makers at NASA before launch (see Feynman as noted in this thread)