Every few years that the HSC is undertaken, a knowledge base of data is created, with detailed information about the housing stock in Northern Ireland (from all housing sectors). For each survey, the final destination of data is the report published on the NIHE site.
Where different addresses have been surveyed across the different years, there is some information that doesn't change (e.g. the age of the property, detached/terrace etc.) This means that data from across surveys could be combined (e.g. the age of houses in a particular area).
Futhermore, NIHE undertook a comprehensive stock condition survey in 2014 which (appears) to cover all of their assets in the social rented sector.