The least cumbersome way of uniquely identifying a business partner being a company, government body or other form of organization is to use an externally provided number.
However, there are quite a lot of different numbers to choose from.
All-Purpose National Identification Numbers
In some counties, like in Scandinavia, the public sector assigns a unique number to every company to be used in every relation to the public sector and open to be used by the private sector as well for identification purposes.
As reported in the post Single Company View I worked with the early implementation of such a number in Denmark way back in time.
Single-Purpose National Identification Numbers
In most countries there are multiple systems of numbers for companies each with an original special purpose. Examples are registration numbers, VAT numbers and employer identification numbers.
My current UK company has both a registration number and a VAT number and very embarrassing for a data quality and master data geek these two numbers have different names and addresses attached.
Other Numbering Systems
The best known business entity numbering system around the world is probably the DUNS-number used by Dun & Bradstreet. As examined in the post Select Company_ID from External_Source Where Possible the use of DUNS-numbers and similar business directory id’s is a very common way of uniquely identifying business partners.
In the manufacturing and retail world legal entities may, as part of the Global Data Synchronization Network, be identified with a Global Location Number (GLN).
There has been a lot of talk in the financial sector lately around implementing yet a new numbering system for legal entities with an identifier usually abbreviated as LEI. Wikipedia has the details about a Legal Entity Identification for Financial Contracts.
These are only some of the most used numbering systems for business entities.
So, the trend doesn’t seem to be a single source of truth but multiple sources making up some kind of the truth.