Thanks Peter. That is just the answer I was looking for.

Hi David,
Looked up Broad Law in Wikipedia which mentions boundary changes- not sure if that answers your question.
Peter

Thanks for the reply Andy but it doesn't clarify the picture. I'm aware most sources give Broad Law as the top. I was looking for someone to explain why Wikipedia is different. Have the Selkirkshire boarders changed at some time?

I have no knowledge of this specific area but I have recently read Victoria Morris' book ‘Highpoints' which was published earlier this year. This covers her walk from John O'Groats to Land's End via the highest point of every county. There was a feature on her walk in Strider 140 (April 2018) and this does mention Broad Law.
The quote from her book reads ‘... the Megget Stone marks the boundary between the historic counties of Selkirkshire and Peeblesshire; Broad Law is considered the County Top of both'.
I don't know if this is any help to you.

Wikipedia, in it's list of Scottish County Tops, has Dun Rig as the county top of Selkirkshire. Many other sources have Broad Law.

Can anyone explain why?