Even the scaled score is not that informative (and perhaps crosses the line on age discrimination) because for older workers the population of people taking the SAT was much smaller as a percentage of high school grads (and presumably weighted towards higher IQs). It's also why there were so many fewer perfect SAT scores -- smaller population in the bell curve.
Yeah, test prep was considered more for people who were worried about low scores. 1500 vs 1600 wouldn't make much difference in college admissions at that point.
Paid test prep is generally considered to be more effective on the current SAT than it was several years ago which also makes it harder to compare across years.
I somehow doubt that the people that would ask for SAT scores would actually be the sort to think about how those numbers should most effectively be used.