Eureka, I found a cool clue!
I must have missed this when my focus on this floor wasn't till after the 3rd floor was reported solved.
I flew out to MD for a week back in June thinking element Mendelevium was the key since its symbol shared a state equivalent like Argon (Ar). The only element to actually have a state name is Cf, Californium, element 98. What I found most intriguing is a strong connection between the forge/mantel rebus "nuclear half life" (in the form of opposites, old-cloudy-death) and the half-life of Cf(iso-250) y=13.08 years. Consider that the Mystery/History video was ep. 308 and the 9th floor future date was 2308, then it seems quite coincidental that 1308 should arise...or this may be just another fantastic reach of the long hand of wishful-thinking.
Secondary theme: Cf, "see F"? Is F a function (math equation) or the music note that corresponds to the color yellow? Back to the yellow arrows...what 7 of those?
12th floor solution
I think the answer to the 12th floor, AR I-40 mile 134 works like this: the state is clear enough with the red circled Mi where Ar is suppose to be, the highway is the rebus of 4-Tea/Tee and the mile is 1 blue, 3 green, and 4 in all. I don't recall anyone every putting it exactly that way so I just wanted to put that out there.
Also, and I'm sure someone mentioned this before, the chalkboard doesn't have a 4. When Quello said the answer is in white on black, he was referring to the pi 3.14 which is just a switched up version of 134.
The buckled 6 was found from this floor. A buckled belt squeezes a squash. Belts are supports. Perhaps we need to look for something that has supports.
just happened onto to this after many moons away,,
Paulo Coelho spent 40 days in the Mojave Desert (40 MD)
I-40 and I-70 intersects just up the road from South Mountain Rest Area (39 31' 29.2N 77 36' 03.38W)
P.K. could also mean PIQUE, this has multiple meanings, not the least of which could be PIKE (type of road) or LEVEL or DEGREE
Quello normally means That ONE or Those Ones.
Oh yeah, I-40 is named Baltimore National Pike
West South Mountain Rest Area is also at Mile Marker 39 (3+9=12)