Feels like there is more to this story given the 22 year gap in the posters coming to market...I wonder how the anonymous builders came into possession of the posters in the first place? The article states the owner of the house had died - did they purchase the house from the estate or family and thus took ownership of the house (and remaining contents)?
Did they buy them (or obtain them) from the family or estate after the discovery?
Or, more nefariously, did they simply take them while performing their 'building' work without the homeowners' knowledge...?