I have two of these lamps and they both have blades. One was bought new by me in 1970 or 1971, the other came from Wheal Geevor and had been out-of-use for several years when I acquired it in about 1974.
I have two compressed fibre helmets. One bears the date 1948 and appears to have been a managers' hat supplied in the very early days of the NCB; the other is much used and came to me from Geevor with the lamp. Both have blade fittings, along with a slot at the top-front of the crown plate for an older type hook-mounted lamp
My former club - Cambridge 4C's - used to have a sack of these helmets, but none survive AFAIK
the electric lamps always had blades, AFAIK and since these started to appear during WW2 and became general by the early 1950s at the latest, I would reckon that by 1950 at the latest all new helmets would have been fitted with blade mountings.
I believe South Crofty converted to all-electric lamps in about 1965 and Geevor by 1970. Certainly when I arrived in Camborne ( 1973 ) there were no carbide lamps to be seen in the mines, and few around - they seemed to have been scrapped wholesale by the mines.
I don't recall seeing any fibre helmets underground in the 1970s, although a few men on top still wore them. The Texolex ones were common ( with the string and leather liner and big bakelite lamp bracket 😉 ) as were the full-brim and cap-style MSA v-gards, which were pretty much the standard Cornish helmet of the time.
I don't ever recall seeing the aluminium ''driller's hat'' underground, I bought my first one in Kingsland's of Yarmouth in 1978 while on my way to start work with Foraky Ltd of Nottingham. I still have it; a full-brim, string-and-leather liner one. I also have a later one, bearing a 1986 date and the clip-in, 4-point harness still used in the Skullgard resin helmets produced today. The cap-style version of the aluminium hats was common in the North Sea, taking the "zero-hood" liner interchangeably with the V-Gard which was also common there.
The aluminium helmets passed out of use by the early 90s, although you still occasionally see them in out-of-the-way places - I saw a Dutch barge captain wearing one in West Africa in 2007, I have seen them occasionally on older platforms in the Dutch Sector and in the Gulf, and one of the drillers at Combe Down had one.
I have one which I bought in Kazakhstan in 2006, a new manufacture one bearing and ANSI stamp - it has a plate riveted inside the crown to pass the single-impact crown blow test required by that standard. There were at least two of these in circulation among the drillers at Combe Down, oddly enough.
''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.