If you use preferred name field in directory in ESS, does this mean HR cannot search by legal name?

Summary:

If you use preferred name field in directory search results (display name) in ESS, does this mean HR professional roles can't search for employees' legal name? This is what we are being advised, however, it seems strange that it is one or another as:

there are sensitives for names for employees may want the wider organisation to know so preferred name seems the obvious choice to use, however

HR will need to be able to search for an employees legal name

but we can't have both? Is this correct? if so is there any way round this?

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