With only one glyph you have to leave the location, come back, shuffle the three cards again and have to try it again.
With more than one glyph you can directly switch to another card either after revealing a dead end or directly after revealing the B,C or D card if you know that this card will lead you to a dead end.
So it's possible to solve this location with one glyph but you have to be lucky since you have to leave, go to another location, come back to location 7, shuffle the three cards again and choose the right one this time. I think this costs you more TU than you have to spare.
Makes sense. Thank you!!