Good point. I have had Global Entry for 7 years, it has worked beautifully every time, except once. I went through the entire process at the kiosk but the machine had a problem with printing and I did not get my receipt. I went through the process at a different kiosk but was rejected as I had already (too recently) reentered the country. I requested help from an immigration attendant and was told I had no option other than to fill out an immigration form and go through the regular line. Fortunately, it was not busy and it only took me about 10 minutes, could have been much worse. You never know.