Good afternoon fotsan,
Here is the long version explanation:
I am using a K5ii + battery grip, mostly with my "walk around" 17-70mm Contemporary. I also own a K-01 ("the brick", not to confuse with the K-1 FF) that I some time use with the 17-70.
Since I purchased my lens in December 2013, with the original firmware (not updated), I decided to test the fact that the focal length was not updated properly, which proved exactly like mentioned in the original discovery.
First, I looked into my Lightroom database to identify pictures taken with the SHORT focal range and found that they were not that great (blurred). There was not so many shots to look at, since I use the lens mostly at the longer focal range. Anyway, I tested it as stated earlier.
So, I decided to buy the USB docking, run the update and test it again. As I did not a very scientific test, I just made sure "the focal value" was updated in the exif data. Of course, the tested image (with SR turned on, slow shutter speed, short focal range) looked better.
OTOH, since I shoot toward the 70mm end, I was surprised to find (SR on) that the focal length was not updated correctly (showing 66mm), even AFTER the firmware update. But it seems the the impact is not much apparent at that FL, since my pictures looks good, and my photography skills & technics improved over the years as well.
My 2 cents:
I wonder why Sigma did not seems to bother correcting the "problem" on ALL focal and stick to what was described in the original problem with short FL. Did they look at it? Did they find out "it was correct"? — I was I little bit disappointed, since I work in the software industry, and fixing PART of FL let me feel "a patch" to me. I don't know if Sigma can do further testing for this.
End of my 2 cents
As far as YOUR concerns:
• for the short FL side, the firmware update made a difference for MY shots
• my 18-55mm kit lens was bought with my K100D (in 2007, K100D only working MF with 17-70mm), an earlier version than yours. And YES there is a difference for me. Never tried the 18-55mm AL II, like yours, to compare.
• without judging you, I don't know your photography skills and I know it's not always easy shooting at slow shutter speed.
Since you own an updated version of the 17-70, I can't recommend what you should do.
May be with a little bit of patience and more attempts, you will find your answer...
As far as I am concerned, I may purchase the Sigma 18-300mm Contemporary lens (since I own the USB docking) for travelling lighter, but there is not much reviews yet.
Hope I my comments gave you some "lights".