My question is, most CRS laws were created prior to or around 1985. Am I incorrect to assume that most haven't been updated since then, or have they? Is this when the standard "1year/20lbs/3years & 30lb booster" minimums came from? I'm trying to establish who's the chicken and who's the egg, I guess (meaning, what came first, the law and the manufacturers followed, or did the manufacturer make the seat first, and the laws at the time reflected those models). Does that make sense at all?
I think what came first was that manufacturers made seats that kept kids in their seats and raised them up so they could see out the window (not very safe). The safety regulations agencies did studies and found that kids could be made safer. They set regulations on how seats should be made and thus the manufacturers made safer seats. Once there was a good supply of these seats in the market and the law makers were pressured, the laws were enacted. These initial laws were probably pretty generic and just stated "use a child restraint" up to a certain age. Rearfacing past 6 months and boosters weren't very common in the 90's.
Most states have modified their laws since they were initially made. Florida might be one of the few that hasn't changed much since their law still only says "3 and younger". Most have added higher age limits to require booster usage. A few have added some rearfacing limits of 1/20 pounds, though many states just indicate to follow manufacturer directions.
I think the main influence in what the laws allow are the federal regulations that the manufacturers have to comply with. When they require 1 year/20 pounds, that is what the seat manufacturers go with. Until those regulations change, I doubt we will see much deviation from what is currently there.
So to answer your initial question, I think the seat came first, and then the laws. The driving force though is the federal regulations the manufacturers have to comply with to get their seats on the market. If we want changes to any laws, we need to get the carseat regulations changed so that manufacturers will be forced to change.