Synchronisation between field "Sell-to Customer No." (Sales Header) and "CustomerId" in "CRM Salesorder"

[mxdevos]

Hello,

can anybody explain to me how the default Integration Table Mapping for the bidirectional Sales Order Mapping can map the field "Sell-to Customer No." (Sales Header) to the field "CustomerId" of the table "CRM Salesorder" as the first field is a code field and the second one is a GUID field, wouldn't that let the synchronisation job fail because of a type mismatch between those two fields?

The "CRM Salesorder" field has also an table relation to "CRM Account".AccountId or "CRM Contact".ContactId depending on the type of the value in the field "CustomerIdType".
The ExternalType of that field is "Customer" which as far as I know can be used when in the lookup in CRM the data can point to a customer or a contact entity.

"Sales Header" > "CRM Salesorder" Mapping

Field definition of "CRM Salesorder" CustomerId field

But I can't quiet understand how the mapping is done when the system synchronizes data between those two fields.
I can't find any code that is handling conversion from "Sell-to Customer No." -> CustomerId, or any logic that handles the assignment.
I found similar code (to what I would expect for the Sales Header/CRM Salesorder) when synchronizing "Sales Invoice Header" -> "CRM Invoice" that tries to assign "Bill-to Customer No." to "CustomerId" but I can not find any code that is handling the aforementioned synchronisation between "Sell-to Customer No." > "CustomerId" of normal "Sales Headers" -> "CRM Salesorder".

Code that handles the assignment of "Bill-to Customer No." and "CustomerId"

So am I missing something obvious for the "Sell-to Customer No." > "CustomerId" field mapping or is it "magically" handling those data synchronisations and assignment of both values.
Someone pointing me in the right direction would be greatly appreciated.