Okay, I noticed that throughout the years the apartment set had been redecorated with different things. Here is what I noticed...

-In the first two seasons they had this orange chair to the left of the couch and then it dissapeared

-The drapes in the back were orange in season 1 and 2, they had white and orange thick stripes in season 3, they had a pink and white pattern in seasons 4-6 and then I believe they changed again but I forgot the exact pattern for the ending seasons, I think it was pink and white stripes or something.

-The lampshade in the back near the drapes was a creamy, white shade in seasons 1 and 2 and then turned to a darker beige pattern for the rest of the show.

-The wallpaper changed (but I forgot the exact patterns) in Janet's and Chrissy/Cindy/Terri's bedroom.

-The landlord apartment below them got completely remodeled from when The Ropers lived there to the time when Mr Furley lived there.

-The couch (the most obvious change) changed in season 8, which was actually part of the storyline for a show.

Anything other things you noticed or any comments?

You've got a good observing eye to notice all of that. I don't notice things like that. I think sets and props change over the years on the majority of shows.