We thank Neil Brenner and Natalie Oswin for their collegial and challenging comments on an earlier version of this paper, and especially want to thank Neil for his generous mentorship and ongoing, unwavering support of our work. We also thank Kasia Paprocki, Jennifer Robinson, Stuart Schrader, Łukasz Stanek and David Wachsmuth for incisive discussions on these issues, and the IJURR editors and three anonymous reviewers for helpful comments.