I have been a custom cabinet maker for many many years, have built my own band saw mill and have dried wood and used it on many of my own projects, and and yes I do think I have a grasp on wood and moisture and wood movement.

And I really doubt if any one can really answer the question,

in my area many many of the home I have worked on over the years are pushing 100 years old, and many have old hard or soft wood T & G flooring, from fir to oak and maple flooring.

In these homes, many of them for the first part of there life did not have even furnaces, only some type of spot heating, usually some small wood stoves, no even heating in many of them over the years,

my daughter and SIL jsut bought a 1930's home with wood floors that had sat empty for 3 to 5 years and even some of the window had been broke out so snow filled some of the rooms, yet the floors (oak) are in really good shape for the situation, jsut some small gaps where the wood crushed, and some darkening, (not sure if jsut a screening would take care of it or not),

In my house there are fir floors as the original floors, and have never seen any noted movement.

But in all my years 30+ in general construction I have never been called into tear out a bad T & G floor.

most floor damage I have seen is dirt, and lack of keeping a finish on it.

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NOW for the actual question,

I read about moisture meters and getting Relative humidity meters and the need for keeping the humidity regulated, and even, and using AC and keeping the temperature even, expecily for new installations,

Have things changed, is the wood that less stable, or is the wood so fresh cut that it is not fully cured?

I guess the question is the OLD time carpenter, many times did not have any more than a hammer and a hand saw, and a nail set, and these old floors are nearly jsut as good as the day they went down, no meters, no stable heating, finishes very elementary, wax or linseed oils or wax, or in some instances NO finishes,

I read about floors bucking and shrinking and everything else it seems like,
Has there been a change? or the new products not worth much? or if you get a good install and product it will last through thick and thin, and those old floors are just ones that have survived?

would like you see/hear your thoughts.

Excellent question... I was wondering the same.

Perhaps quarter-sawn wood was used more extensively in flooring back then.

There are many reasons one can attribute to the phenomena of which you speak. I'll address older homes first.

These homes were built with old growth lumber. It is common knowledge that old growth wood is more stable due to it's tighter grain patterns and slower growth. As far as flooring, the old floors were hand nailed. This did not draw up the wood as tight as machined nailed floors do today. So there was a built in expansion, similar to laying gyms. The nails used back then allowed a certain amount of give, enabling the flooring to expand without buckling. And as another poster mentioned, much more use of rift and quartered wood. I have worked on many older homes floors. I commonly see gaps between the boards and lots of noise/squeaks. IMO, what often happened was at one point, the flooring expanded but didn't buckle due to the give of the nails. Then at another time, shrank. That left the gaps. Now the flooring is free to move without cupping and buckling regardless of temps or humidity.

Now new homes and floors are way different. The wood is second and third generation and nearly all plain sawn. This type of wood is not nearly as stable as the old growth, nor is it typically as hard. It is also installed with cleats or staples, which hold way better than nails do. When the flooring needs to expand, the fasteners hold it fast. Then one gets a cupped appearance from compression set. Customers today will not accept a floor with gaps or noises, common with old floors. The trade-off is a floor more susceptible to cupping. But the good news is we have HVAC systems that work quite well and can maintain a year round comfort level for the occupants. And it just so happens that the same temps and humidity levels humans find comfortable is also the ideal levels for floors. BTW, this applies to fine furniture and antiques as well. Most museums are temp and humidity controlled, as are some historic buildings, like Hearst Castle at San Simeon, CA. It is not difficult to maintain moderate temps and humidity levels in a more modern home. My house was built in 1986 and is typical insulated wood frame construction. I have central heat and air. My settings are no lower than 60 degrees (when I'm gone in the winter) and no higher than 78 degrees (summertime AC setting). This keeps the humidity in my home a comfortable 45 to 50 %, which is ideal. Also, it is completely dry under my house. So, it isn't difficult to keep the temps and humidity levels within recommended levels. Some areas may need humidifiers or de-humidifiers. There are low cost portables for those not wanting to have a central unit installed.