mark,
There is no requirement for how you do it. Address it as you will in your Written Practice (though you don't even need to do that)and then follow that.
Just keep in mind, you will need to get it passed an auditor, so being lenient upon yourself is fine, but there is a limit.
Your written practice should detail those particulars. Are you attempting to write it?
Keep in mind SNT-TC-1A is a list of recommendations. Should does not = shall, recommend does not = will.
As to your question, the correct verbiage is 'outside agency'. Also remember a written practice is only one part of a QA program.
As JS55 mentioned, if your performing code work, your likely doing so under a QA program. That invokes a host of issues, not least of which is many countries insert their own laws and rules that are above and beyond your QA program. Auditors/third parties will be around to assure you comply.
TC1A may be a recommended practice, but those additional requirements must be covered.