This article refers to calibration with historical timelines, it is not about things that occurred 5000 or 10000 years before anything was written down.
This is the same as the one before. Here's one juicy quote "By measuring the amount of carbon-14 in the annual growth rings of trees grown in southern Jordan, researchers have found some dating calculations on events in the Middle East – or, more accurately, the
Levant – could be out by nearly 20 years."
They're worried they can't date things to 20 year accuracy, no one claims to know when a particular boulder was deposited by a glacial flood by that level of precision. (Again it is thousands of years earlier than the period of "low accuracy" being questioned here.)
Global warming *might* mess with our ability to date things from the industrial age, confusing them with 2000 year old things. This has no impact on ancient things at all.
Where are you seeing any claims of dating flood deposits in the PNW based on molluscs?
Most of these are irrelevant to the dating of the ice age floods and the only one that is even close (molluscs) is a WELL KNOWN ISSUE. No competent geologist is going to take a raw date from a deposit of mollusc shells and use it to date something directly. (Perhaps, since it give overly old ages, it could be used to define an upper limit if no other material was available to date.)
As for your general "complaining" about the broad nature of the dates, these are not a single event but many occurring over a couple thousand years. Different individual floods inundated different parts of the region, etc. A variety of dates should be present even if every flood deposit could be dated to 100 year accuracy.