Hey, don’t listen just to me. How about these reputable endorsements for the girth hitch master point?

Ortovox (a German company best known for avalanche transceivers and related ski mountaineering gear) has an excellent Youtube tutorial video series on many aspects of mountaineering. The video series has the (somewhat awkward) title of “Safety Academy Lab Rock”. It's produced in partnership with Petzl and the German Mountain and Ski Guides Association (in German, “VDBS”). So, you can probably assume that the techniques shown have technical approval at the highest levels.

The video below shows various VDBS guides building multi piece anchors using an open (aka untied) cordelette.

In every case, they use a girth hitch to create the master point.

(The climber in the video is also using two techniques uncommon in the United States: 1) using an overhand knot to make a loop from his cordelette; and 2) threading the open/untied cordelette directly to the pitons / protection without using carabiners.)

Watch the video below. (The whole video is only 3:30, but if you have a short attention span, start at 1:00 and 2:00. )

Note the girth hitch at the master point in the thumbnail image below (and yes Eagle-Eye, this is for a four piece anchor.)