@Common Threads
You actually see the stairwell 5 times -- here is all my evidence that it is the same:
Season 1 episode 8 -- at about 18:32 - this is Hopper sobbing on the stairwell. there is no door. the steps are reddish brown with some sort of texture. The floor on the landing has square tiles.
Season 2, episode 8 at 13:56- Bob goes to the basement. You cannot see the steps clearly but there is no door on the landing that Bob passes. The handrail appears to be the same.
Season 2, episode 8 at 16;56 -- You see the steps - there is no door on the landing. the rail appears to be the same. The steps are dark colored and have texture of some sort. The landing appears to be tile, but this is hard to see.
Season 2, episode 8 at 17:26 - the hand rail appears to be the same, the color of the steps appears to be the same dark reddish hue, We get a glimpse of a landing -no door.
Season 2, episode 9 - an extended sequence starting at about 28:30.
At 28:31 we glimpse the steps and the hand rail - the steps have the same dark red and the hand rail appears to be the same.
At 28:36, as Hopper goes around the corner he says "oh, s---t", it appears he is turning the corner on a landing - there does not appear to be a door behind him.
At 28:39-- we see El standing on a landing - we see no door behind her...
But we do see a door by Owen, who is lying on a landing.
Conclusion: most stairwells do not have a door at every landing -- usually they alternate between door/no door on landings. I believe that the stairwell in the hospital and the stairwell in the lab are the same. What is unresolved is whether (a) they used the same stairwell for convenience in filming and thought no one would notice, or (b) it was intended as a clue of some sort - that Hopper was at the lab before...