For my trip the beginning of this month I booked EBCI for myself, grand-daughter and my son's mother in law. I booked my flight in June, and booked EBCI right away. in July I was able to convince my daughter in law to let me take my grand-daughter as long as her mother came with us, no problem, I booked their flights and the EBCI.
Fast forward to getting our boarding passes, on the trip down my grand daughter was a-24 and the 2 grandothers were a44 and a45. Coming home my grand-daughter was a22 and we were in the 40s again.

We all boarded with the 40s but I thought it was strange that mine was not the lower number and the 2 flights that I booked a month later would have been higher.