Alright, I'm sure MANY fellow old house owners have found themselves in a similar situation. You decide to start picking at something only to end up with a huuuuuge job that ends up taking 10x longer than expected. This is sort of the case with this post, but I've decided NOT to fix the problem for several reasons...
It all started when I just wanted to scrape-down the excess putty left on the wall after I had removed the drywall column (cold air return) in the living room. See this thread for info on that: http://my1923foursquare.blogspot.com/2011/10/major-october-update.html
When I started to scrape, however, a few pieces of paint-covered wallpaper tore off with it. I decided to keep tearing a small section, and then I ended up with this:
As you can see, I uncovered MANY layers, and with it, revealed some old wallpaper, several different paint colours, and even the ORIGINAL colour!
The rather bright peacock blue that you see in the centre here, is the original CALCIMINE paint over the original drywall (the brown scrape in the centre is the drywall paper).
You can also see one original wallpaper design, along with a rather small top border (no more than 3" wide). The colours on it are rather pale greens, oranges, and beige.
There's also some of that wonderful mint green that seems to be found in ALL older homes.
Now, I probably COULD fairly easily scrape down both exterior walls down to the calcimine blue, but then I'd have the problem of trying to paint over it. Apparently not much will stick to it, so I could end up with some major problems. Another issue is that I've already repainted and caulked (and generally beautified) both windows, and if I were to scrape everything down, I'd probably end up screwing-up all the edges with chips and peeling bits. Not to mention all the work.
I'm also sure you noticed the large (unevenly sized) holes that they made for the blown insulation. For a long time I've wondered how it was done (from the inside or the outside) but now I know. The patches aren't expertly done, but the walls are just so uneven and bumpy that I never noticed the holes were there. I'll have to re-patch those two properly.
So yeah, this is one project I *WON'T* be tackling. I'm just going to putty over it and ignore it. I do want to be DONE with renovations at SOME point. *eye roll*