Just from the photo, I suspect the foot was applied to this vase while it was still on the blowpipe. A finisher at the bench (the chair in UK terms) used a tool called "clapper" or foot squeezer to shape the foot, and the result is often a bit uneven as described. If the vase was then was cracked off the blowpipe and taken to the lehr, the top area would be finished (ground/polished?) after annealing. How is the top edge of this vase finished? In this type of operation, there would be no gadget (called "snap" in USA) used at all. So, I think the Y-shaped mark is the result of cutting off the bit that became the foot when the tool was used to shape it.
Also, the mark that looks like "fiber" could be from a lehr pad, i.e., fabric used on the chain-link metal belt in the lehr to keep the piece from being marked by the metal. If the glass is very hot, it will pick up marks from the lehr pad.