[SalesForce] Salesforce CPQ: Using CPQ API to Reconfigure an existing Bundle in an Amendment

I don't think there is any need of checking the API. What you can do is,

    1) Query the Product Option object and see if the product you are trying to add as the line item is a Configured Product on any of the options. Save it in a map.   
map<ProductId,ProductOptions> mapProdOptions 
    2) Then, before adding the product as QLI, check if the map.get(ConfiguredProdId) is blank and if it is NOT blank, get all the Optional SKU products on the product option and create Quote Line Items for them along with the main product

Most probably the problem is in the order of execution of your code.

The onBeforeCalculate (and other event handler functions) return a Promise so that the calculating engine can wait for one, to finish processing, before starting another.

But in your code, you are starting a Promise (conn.query()) but exit from the event handler immediately with return Promise.resolve();

What you probably want is to return the promise in the event handler: return determineValidHistoricalPricing(...) so that the flow actually waits for your logic to finish.

Update: CPQ requires its event handlers to return an actual Promise object (and not a promise-like JSForce connection), so for the above to work one must also wrap the JSForce query in a standard Promise, like so:

return new Promise(function(resolve, reject) {
    conn.query(queryString)
        .then(function (results) {
            // ... processing results ...
            resolve(results);
        });
})