Similar to any NDT method, you could always use a sample or test piece. Essentially perform a variation of the inspection they will perform daily. (Ex. we utilize a scrap machined nozzle and the potential inspector has to identify the discontinuity and/or dimensional errors)
as for "we done this, this way for 40 years, that is not necessary" mentality. - Explain to the stakeholder the benefits of a potential change (if you see a benefit of this suggestion)