Alternates are chosen by the highest eligible skater starting this season, no going down the list of top 10. Fabbri/Ayer happened to be at the top of the list since apparently they're updating the alternate list with current SBs if they're higher for most of the skaters. The official list is here, last updated October 8th.Do GP assignments normally work like that? Isn’t there usually a replacement list or something?
It was a nice coincidence that they're located close enough that they could be alternates with little difficulty in travel arrangements and shared coaches with other teams.