Interpretation of original material from companies is fraught with difficulty. It invariably reflects the perspective of the current owners and can often be economical with the truth. Although sometimes the truth is written in such a way that the reader infers something else, so always quote complete, exact wording and punctuation. Omissions can be significant too, try finding mention of O'Broin in Caithness company literature since he left the company!
The PO Box number will reveal nothing useful, other than where Paul would collect his mail from.
The worst source is often the tales told by people that have worked with the subject of research and this is a big problem with the Ysart's - many people claim to have worked with, been buddies with them and tell some amazing stories. Some of which continue to circulate and grow richer. Nearly all have been disproved over the years.
Safest approach is to always be sceptical and look for secondary sources and/or time related facts that are 'more likely' to be accurate. This leaflet is a good example of spin, but it is also ambiguous in time. The full text might say more.