the chisel tip ones have replaceable bits, but they were sometimes discarded instead when they were worn past sharpening. The sheer numbers of them used over the years meant that there are quite a few around, they were used for a variety of jobs above ground.
the taper-ended ones would simply have the old bit knocked off and a new bit fitted, and would be used until bent or the chucks worn beyond service.
the rope-threaded rods on diamond drills and drifters could remain in use for many years.
hard to find much out about this, but Trounson 'Mining in Cornwall' Vol 2 fig 27 shows a group of miners at Wheal Carne in or around 1900 with a stoper drill which appears to have an integral bit. Vol 1 fig 77 shows a miner at South Crofty shortly after WW2, using a stoper of pre-war design and the steels stacked behind him appear to be integral bits, although it's not clear in either picture.
my best guess is that integral steels with tungsten inserts date from the 1930s, and continued in parallel with the knock-off bit type until the present
''the stopes soared beyond the range of our caplamps' - David Bick...... How times change .... oh, I don't know, I've still got a lamp like that.