This is the page marked with ref 2 of the Kowloon streetmaps. Note the Prison of War Camp next to Kowloon Hospital on either side of Argyle Street.
I have now amended the title to Boundary Street to eliminate confusion. I did have a look at the map in magified form and it was marked Boundary Street.
I have done a bit more research to find out why it was referred as Boundary Road in an unaccompanyed note that I have. I must say the information in the note was rather confusing. So rather than trying to dig deeper, I will just put it as an error on my behalf. All good now.
And thanks to Megabyte for the authenticated information about Boundary Street.