Thanks both - I did wonder about Type 4 Tiger's, but the white is base glass rather than a veneered ribbon, and I think the Type 4's were veneered white on opaque white.
Not that it's a reliable guide, but they came with a bunch of All Reds (non-blackline) that looked 50's/60's colouration and both vaned and very whispy cages (in pale shades), so I was leaning pre-Gladding. Could be later and just mixed together of course. I don't think they're dug - the veneer fracture damage looks like some kind of problem in the cooling (the camera exaggerates what they look like in the hand). No other colour combinations in the group.