There's an answer that would theoretically address this issue, but the code doesn't seem to be effective - possibly because it's not meant for use with a book class document.
What I'd like is to display page numbers alternatively in the bottom left and right corners, and the code below uses fancyhdr, but the page numbers are being rendered alternatively in the left margin and the center. Even being in the left and odd in the center (or apparent center).
\documentclass[11pt, twoside]{book}
\usepackage{geometry}
\geometry{letterpaper}
\usepackage{pdfpages}
\usepackage{amssymb}
\usepackage{fancyhdr}
\fancyhf{} % clear all header and footers
\renewcommand{\headrulewidth}{0pt} % remove the header rule
\fancyfoot[LE,RO]{\thepage} % Left side on Even pages; Right side on Odd pages
%
\pagestyle{fancy}
\title{Another Book}
\author{An Author}
\date{}
\includepdfset{pagecommand=\thispagestyle{plain}}
\setlength{\footskip}{114pt}
\begin{document}
Is there something that's overriding the \fancyfoot code?

\includepdfset{pagecommand=\thispagestyle{plain}}? I guess that it could be the problem. Try to comment it. – Sigur Dec 19 '14 at 22:15bookclass. You need to redefineplainas well. – Johannes_B Dec 19 '14 at 22:20\includepdf, or are you creating a document from scratch? – Werner Dec 19 '14 at 23:00lilypond. The numbers on those pages are also showing up centered, but that I imagine needs to be addressed separately. – MikeiLL Dec 19 '14 at 23:05