The gradual accumulation of information in our database, as described under Data Collection Method, was accompanied in parallel by validation of the source material. As various museum datasets were incorporated into our own dataset, the existing data was either corroborated or contested. In the latter case, we contacted the museums or cross checked with other sources as required to resolve the disagreement in the data. 

When a data source was old or the date of the source was uncertain we checked if the museum was still open. In some cases museums that have closed still have an extant website so we looked to see if news and events pages had been updated. TripAdvisor was also useful as it records when visitors went to particular sites, and hence indicates whether it is open or has possibly closed. This approach was also used, to a lesser extent, with smaller, specialised web-forums where contributors occasionally posted questions or reminiscences about particular museums.

The Museum Development Network provided robust external review of our data. We took regional data to each of the nine Museum Development groups in England, and they conducted a line-by-line scrutiny of the data.  They were able to provide a local knowledge of both recent developments in their area (openings or closure) and to check our classifications. Staff at the national offices for museums in Northern Ireland, Scotland, and Wales similarly scrutinised the data, as did some specialist and subject groups. We provided our full dataset on regimental museums to the Regimental Museums liaison officers at the National Army Museums who provided comparative information, which allowed us to re-check that sector, and our dataset on transport museums to the Transport Museums Trust who further edited and refined data on museums from that category.