Process for adding a new AP vendor with the same Tax ID as another vendor in R12.2.9

Hello,

Does anyone use the workaround functionality to have multiple vendors in AP with the same tax ID? I followed the instructions in Doc 1135593.1, confirmed that we have the patch and correct version as noted in Doc 2710040.1, but when we add a new vendor with the same number as an existing vendor, we're still getting the "This tax registration number is already in use for party type" error.

So just to clarify, we add the dummy tax with the "Allow Duplicate Tax Registration Numbers" box checked to the existing vendor, yes? When we want to add another vendor with that number, we enter them in AP as a new supplier, and we should be able to add that same tax ID, yes? Am I missing a step?