The Coupa Supplier table has two Commodity fields - one for Default Commodity and one for Preferred Commodities. The Preferred Commodities field is missing entirely, despite being included in API responses.

Additionally, Commodities are a hierarchy, via a Parent field on a Commodity record. In the REST API, there is not an endpoint to query Commodity directly, it only comes as a sub-object on another record such as Supplier. Currently only the first-level Commodity is getting saved to my destination, and not any parents of that Commodity, so unless a Parent is the first-level Commodity we lose the hierarchy. 

As an example, a Supplier has the following Default Commodity data via the REST API, but only Commodity ID 70 gets saved to my destination (unless another supplier has Commodity ID 12 as a first-level ID).

"commodity": {
    "id": 70,
    "created-at": "2018-03-21T14:55:51-05:00",
    "updated-at": "2020-02-03T10:47:00-06:00",
    "active": true,
    "name": "3rd Party Logistics",
    "translated-name": "3rd Party Logistics",
    "parent": {
        "id": 12,
        "created-at": "2008-11-25T11:18:33-06:00",
        "updated-at": "2020-01-10T10:37:58-06:00",
        "active": true,
        "name": "Transportation/Logistics",
        "translated-name": "Transportation/Logistics",
    }
}

You can query the Commodity table directly via the GraphQL API, and this would probably be the best way to ensure that all commodities get synced since you wouldn't have to deal with the hierarchical structure.