Miles apart even for the ones just found in Wales. There would be a small community of miners operating a single rock type. Originally these communities would just be concerned with the local need for slate/stone, successful operations with good trade routes could meet demands in local towns/cities or even for export. Exceptional rock regardless of how remote would be in demand as well.
A lot come from the Snowdonia area, but then you have rocks from Yorkshire, Leicester, Scotland and Devon/Cornwall as well. The hones were produced in quarries that were mining for tiles, roofing slates, building blocks and aggregates. The hones are often just extra income, In a similar way to how Inigo Jones currently operates.
Inigo Jones Welsh Slate Gifts and Products Slate printed wall plaques for sale by Inigo Jones
Saw marks are an industrialisation thing. There is a point when hones move from cottage industry to mass cut items. Each quarry would have a different way to cut the rock. With machinery and saws been hand made. This is why saw marks can be telling as there were no off the shelf blades.
WW1 would have put huge demands on hone producers and forced modernisation. Before WW1 full beards, moustaches, and sideburns were common both on and off the battlefield. WW1's trench warfare put shaving at a priority to ensure your gas mask fitted correctly. You would issue rocks and razors like water, They would get cracked/broken/lost in the field and the conveyor belt of troops, deaths, and equipment issue meant that hones needed to be cut fast, well packaged, Available in bulk, and work well enough for a close shave.
The UK's army would have mostly been using straights as these were still in issue at the battle of the Somme 1916. In contrast the USA forces were issued with saftey razors by Gillete.
Military kit through the ages: from the Battle of Hastings to Helmand - Telegraph