During a work I sent over an IPTC stationery preset to a colleague to use on his computer. I have all IPTC fields visible, but he has just the most commonly used ones displayed and he have hidden the rest of the fields.
If the IPTC Stationery Pad data is set to apply fields, then they will be applied whether they are seen or not by you prior to their application. One can apply an IPTC Stationery Pad from the Contact Sheet outside of the IPTC Stationery Pad.
To be more clear, what I mean by "fields that are not visible are never overwritten" is data that is not capable of being edited by the IPTC Stationery Pad. For instance Adobe Camera RAW settings are never editable, and they are always preserved.
You gave your colleague an IPTC Stationery Pad set up the way
you wanted it applied and when your colleague used it, it did what
you intended.
-Kirk