Once upon a time a pilot turned down a ship because it was a few inches over the limit. The next pilot in line called horseshit and took it up to the dock. The first pilot felt insulted and brought charges at the next group meeting. After much heated debate a proposal was made to go by rounding the dimension to the nearest foot. By the rules of the organization a supermajority was needed to allow a change to the rule. We did not get the supermajority.
It’s complicated sometimes.
And who exactly benefits from that bit of absurdity? It makes the pilots look like fools and just embitters shipowners and shipping companies against the pilot organization and the port itself. Sounds like a bunch of entitled children.
Pilots are the subject matter experts for their port/district. While the ships are their “customers”, they also have a very real obligation to protect the port infrastructure and local waterways. Anyone who thinks they know better is welcome to try it themselves (yes, I know that’s not likely).
It’s not generally in pilots’ best interest to turn down business so if there is a limit of some sort, there’s likely a good reason and, perhaps, a hard lesson learned sometime in the past that led to that.
Without texastanker naming the port, it’s hard to know the logic behind it. It’s entirely possible that 820’ limit was crept up to from, for example, 750’ (maybe a turning basin is involved). The line eventually has to be drawn somewhere.
Understand and agree - If it was easy there would be no need for this chat !!
By the way - there is no “right” answer here to this one - not a math problem - I think I understand the drives of all the players, and in the end believe all are just trying to do their job.
Agree - well except for there has to be a " hard line". I have seen places were the were hard lines - ships berthing head in with a Bow - Manifold diff that was a hard line, i know of at least one berth with a rock shelf astern were stern to manifold is a hard line.
But you can never - ever convince me that 1 inch of LOA on channel transit needs to be a hard line - again - no one even knows the actual length of that ship on that day to that level of precision. The hard line, in this case, is to take it out of judgement - make it consistent and avoid a continual push up - but an inch ??
I had to smile reading that, both those tricks work well on sailboats too and I have done them many a time. On boats with folding props frequently reverse thrust is poor and the forward-wiggle thing is the only way to break suction so you can back off.
At super-low tide I sometimes have to wiggle my way into my slip, I am about half a foot in the mud at that point.
I bet the ships change length several inches in the hot sun 
I think that the group could publish it something like this -
Max LOA = X, all vessels over X require prior approval on a case by case basis.
It’s not you that one needs to convince, it’s the lawyers.