Even so I'm not convinced about the distinction of swerve from side spin and swing achieved thru seam position was not present in the golden age. Those who achieve movement via side spin are usually slower bowlers than those who achieve it from seam position. Noble as an example.
From what I've read Hirst was much quicker than spinner/swervers like Noble and is credited with getting swing thru the air by more moderm means. This would gel with his reports of his faster pace. Hirst himself was never forthcoming how he did it but he did coach players in his later years and they definitely were swingers in the modern sense.