There is a lot of talk today about what is "natural" as opposed to what is synthetic; "natural" suggesting a special level of goodness. Perhaps the great irony here is that what you might call the "international standards" for essential oils were set by chemical (aroma chemical) companies who saw little difference between the two except in the nuisance of purchasing and processing and the profit each produced.
Dodge & Olcott, which traces its roots back to 1798 in New York City, remained a family owned business for 150 years. Starting as an importer of oils and pharmaceuticals, Dodge & Olcott branched out into manufacturing some time after 1850. (They had manufactured gin, whiskey and "spirits" for perfumers early in their history -- but this business was discontinued after a fire destroyed their Brooklyn, New York, plant.)
From the point of view of essential oils, the company was purchasing from sources all over the world, many of which were operating under very primitive conditions where no reliable banking facilities existed, communication by mail was slow and uncertain, and transport of goods involved risky ocean voyages.
Around 1839, one of the partners (Wheaton Brandish), on an essential oil seeking sea voyage, was shipwrecked, presumed drowned, and, after a number of months had passed, was written out of the partnership. When he turned up alive, after having endured a great many hardships, he found he was out of a job!
It was through the risky business of ocean voyages and meetings with foreign sources that Dodge & Olcott knew what they were buying (the nose was the test!) and who they were buying it from (checks on the integrity of the seller). For their part, Dodge & Olcott had such a reputation that their word was trusted and much business was done without the conventional letters of credit. In short, they weren't in the business of buying and selling garbage. If you bought an essential oil from Dodge & Olcott, you could be sure that you were getting what you paid for.
Fritzsche Brothers, although it was launched as a subsidiary of a German chemical company, also became a leader in the American essential oils market.
It was Fritzsche's Frederick Henry Leonhardt ("Fritz") who commissioned Dr. Ernest Guenther (a master plumber!) to spend twenty years of his life studying essential oils globally. This study resulted in Guenther's 6-volume classic, "The Essential Oils." Again, the issues were quality and consistency. Fritzsche, like Dodge & Olcott, (the companies later merged) was dedicated to giving its customers what they had paid for and a bottle of Cade Oil (for example) purchased one year should be as little different as possible to a bottle of Cade Oil purchased in another year -- a very difficult proposition in the late 19th and early 20th centuries.
This emphasis on quality and consistency is a reminder that the perfumer requires that when his or her formula is scaled up from a "trial" to a bulk order, the aroma and other characteristics of the perfume must remain consistent with the trial. The ODOR QUALITY of the essential oils (and any other materials) used in the laboratory versions must match those used in production. It is not such an easy task but if different grades of the same ingredients are used, the result for the perfume marketer can be DISASTER!