Hi Patti, I think the clothing for the 1990 DS actually got closer to what was worn in 1790 New England. I seem to recall having read that the costumes for the 18th century sequences in the original Sixties shows came from work that had commissioned for a production set in the mid 18th century. I'm not an authority and it would be interesting to know for sure.
I always think the Countess's clothing in the 1967-68 shows was way out of date, more 1760s than 1790s, although I love how Grayson looks in the clothing.
The main 18th century costume that just does not work for me is what they gave Barnabas to wear. I'm sure it was researched and was accurate but it just looks awful on camera, particularly in combination with the wig and the makeup.
Of course tastes differ--just giving my opinion.