I can't speak to what those dates mean. Does it mean those batteries were in use in vehicles already at the time? They were available for sampling only? Ready for mass production? In mass production?
https://www.greencarreports.com/news/11 ... production
from Feb 2016 says
The cooperation was formally announced more than four years ago, in August 2011, by GM's then-CEO Dan Akerson and Juno Cho, president and chief operating officer of LG Corp.
Funny enough now that you mention the time, it took Jeff at https://electricrevs.com/2018/07/17/wat ... -to-55-kw/
60 minutes to get from 12% to 80%,
https://www.torquenews.com/7893/3-takea ... ery-expert
item #3 gives a bit of color...
On the reasons for the Bolt EV's fast-charging limitations, however, Piper did provide a little more insider knowledge, stating:
"When we first introduced the Bolt EV back in 2016, our goal was to build the first affordable, long-range electric vehicle. At the time, we optimized the system components around the battery, e.g. cables, contactors, and so on.
"Higher current requires bigger, more expensive cables, etc. and ultimately you reach a point of diminishing returns in terms of saving 10-15 minutes during the occasional DC Fast Charging session versus needing to pay for a more expensive battery system."
In essence, he's saying that GM batteries were more expensive at the time and GM had to keep costs down.
This doesn't preclude the idea that the engineers could optimize the battery management to get closer to a 1C rate on the 2020 model, which would put the maximum rate closer to 65 kW, but the company clearly doesn't see improved fast charging as a primary concern at this point in time. Note the "occasional" and "diminishing returns" terminology when discussing time savings, for example.