I have some of these beads as well, and tried replicating some by lampworking. Wgen looking at them up close, I had noticed that the white lines were always parallel to each other all the way through. Was pretty impossible to recreate by lampworking. Could not understand their procution method.
Them being from mosaic blocks makes me understand the concentric parallel lines. Looking at mine up close, I think some are indeed only cold worked, and some have seen some heat at some time. Some actually have the corners ground off, making them 'cornerless rectangles'.

Mine came from two sources: a mixed strand of mosaic Roman and Islamic period glass beads and fragments bought in Tucson, and some from a mixed strand of all sorts of beads bought in Iran.

The red molded glass beads are indeed still being made in Czech. Was once at a stand of a Dutch dealer where one buyer was also convinced they were ancient. I had a picture of a full Islamic prayer set made form Czech beads with me on my iphone, and that sorted the debate quickly.