This is exactly what I was saying.

It doesn't matter if you measure LNG in litres, gallons, or cubic inches. The market is going to pay you the precise amount for whatever you delivered measured in cubic meters. So what you measure in is irrelevant. Or more precisely, only relevant insofar as you want to have some idea how much you are going to be paid when you reach the market. And even then, it's only relevant to you. The market doesn't care what you measure in, because the market measures what you deliver in cubic meters. And the market has its own definition of "cubic meter".

So market participants, no matter where they may be, are incentivized to ensure whatever unit they're measuring out for delivery in will relate to the "cubic meter" as defined by the customer in a precise and verifiable way. If not, they could lose money. Thus, every freight measurement standard, would, again, effectively be set by the customer. Because no matter what units you deliver in, s/he is only paying you for the amount measured in his/her own measurement standard. So your standard has to conform to that standard in a fashion that is well defined, consistent, and well understood by you.

In ancient terms, this means the trader in Mohenjo-daro would have calculated that conversion factor out in a precise fashion. So they would walk around Mohendro-daro with a standard weight for measurement that was based on what they would expect to happen in Sumer. All the other traders in Mohendro-daro would eventually discover the same conversion factor. So everyone lands on the same weight for measurement, but no one collaborated. Because everyone, (every trader anyway), only cares what they can get for that weight in Sumer. It's not that everyone uses Sumer's units. It's that Sumer's units define what everyone's understanding of their own unit is through trade.