"Some people use it to describe a specific genre of music that either came into being in the 1970s or the 1990s, depending on who's doing the telling, that tends to the introspective."

Yes, it did "come into being" during the 1970's. Artists like James Taylor, Harry Chapin, Joni Mitchell and others were described as such - but it was more likely to hear them called "folk rock" during that time period.   During the 1990's, that was replaced by "singer-songwriter.

As to the "sensitive" and "introspective" tag - that is merely a stereotype. Yes, songwriters will tend to write more personal songs - but many traditional songs are also intensely personal so to add that description to all singer-songwriters is equally incorrect.

It is amazing- where once we had discussions on "what is folk", I can see it changing to "what is singer-songwriter". At the end of the day, as Spleen Cring points out - it really doesn't matter.