They actually didn't - its all in the hidden text on the Category link on the respected Name study pages
The Sweetman name study was indexed by Staffordshire - where as the Stanton name study was index by Stanton / The forth letter of each being 'f' and 'n' respectively - as f comes before n - then Sweetman was listed before Stanton
I have now changed the indexing so that they are in the right order.
To change the indexing order of a link you would add the category (in this case) [[Category:Staffordshire, Sweetman Name Study]]
then add after Name Study "|Sweetman" to force the indexing not to index on Staffordshire but on Sweetman