I like to call this "laparoscopic cabling." Just FYI, this location being an exterior wall makes it extra challenging!
Study the building a bit:
- Figure out the height of your 2nd floor's floor joists. You can do this by measuring vertically between a pair of windows outside, then subtracting the height of the walls inside. Depending on the design of your stair case, it may be possible to measure indoors from 2nd floor to 1st floor, then subtract the height of the 1st floor ceilings.
- Confirm that the walls in 2nd floor and 1st floor are the same thickness (is the casing on the sides of the window the same depth upstairs and downstairs?). If they're different you'll need to account for some offset.
- Verify that your work on the two floors really is aligned. Measure from the adjacent exterior wall ("around the corner" from where you're working), add any offset if there's a difference in thickness of the wall framing.
Insert the glow rod from the first floor going upward. A sharp, stabbing motion should persuade the glow rod to penetrate through the insulation. Use your knowledge of the height of the floor joists overhead to measure as you do this and confirm that the glow rod went in far enough to reach the bottom side of the subfloor above. Secure the glow rod so that it gravity won't pull it down when you walk away. Tip: I always tie a loop in some mason's line and attach it lightly with tape to the end of the glow rod. That way, when I finally lay eyes on it with the borescope (to which I've attached a hook positioned in view of the camera), I can use the hook to grab the loop and pull the string through. The string is then used to pull the cable.
Go have a look into the joist space from upstairs with the borescope. If this were an interior location the insulation would be laying horizontally just above the ceiling, likely with some air space above it. Because this is an exterior wall the insulation you're hitting is probably installed vertically pressed up against the rim joist. Hopefully the tip of your glow rod will have exited the insulation and will be visible on the camera, but you may not be so lucky.
And.. hopefully that gets you through. If there's no sign of the glow rod, double- and triple-check your measurements to be sure your 1st floor and 2nd floor work is aligned.
Rim joist insulation could cause you a lot of grief. As an alternative to the glow rod, try some stiff wire. Steel, like a coat hanger, is better than copper because it's stiffer. Bend it into an arc. Orient it so that when the wire is inserted that through the hole at the top of the 1st floor wall and continued through the hole in the top plates, the tip of the arc will exit the rim joist insulation and be visible in the open joist cavity.
One parting idea: the upper room has carpet. Pull that back away from the wall in the corner where you're working and drill a hole through the subfloor a few inches in front of the wall. This gives you a new vantage point from which to view the joist space with your camera. That may help puzzle out the solution. When finished you can reattach the carpet, covering the hole without any need for repair.
And.. you're right. There can come a point at which you'll be faster to just cut a hole in the ceiling and repair it rather than continue the fight with the fishing.
Edit: and now, more thoughts..
You have vinyl siding?? Why didn't you say so?! :-) There are a hundred different ways to route and conceal UTP cable on or in a vinyl-sided wall. Admittedly, one should use outdoor-rated cable for this though. The trim that runs up each corner of the house has a nice big gap into which the cable may easily be pressed. A cable running horizontally beneath a lap line on the siding disappears fairly well; you could also run cable horizontally behind the siding almost as easily. The cable could emerge from attic to exterior, then surface route down to where you want the camera to be. You can even use a siding removal tool to "unlatch" one course of siding from the next, giving you access to route the cable behind the siding.. or to cut holes in the sheathing for easy and restoration-optional access into the wall cavities!
I might cut enlarge one of the drywall access holes to be about 24" tall and use a 36" drill bit. This gives room to drill through the first wall plate and then get the drill into the wall so there's no bend in the drill bit. You can then be more confident about drilling blind through the other wall plate with good placement and angle.