Memoir pagestyle problem

Question

For a memoir document, I'm trying to get even and odd page headings for ordinary chapters to have the forms such as

2                                          1 One

and

1.1 A section                                 3

where "2" and "3" are page numbers, "1 One" is the number and name of the chapter without the word "Chapter" or a period after its number, and in "1.1 A Section" there is no period after the section number.

I thought I'm doing what was shown in https://tex.stackexchange.com/a/512366/13492.

I'm also using special headings for frontmatter and backmatter, as shown in the source below.

Questions:

1. Why is \pagestyle{main} seemingly ignored starting on output pages 2 and 3? The headings produced seem to be defaults.

2. Why does "Guide to the Literature" in the back headings disappear from the final page?

Sample source:

\documentclass{memoir}

\setsecnumdepth{subsection}
\settocdepth{subsection}

\nouppercaseheads

\makepagestyle{main} 
\makeheadrule{main}{\textwidth}{\normalrulethickness}
\makeevenhead{main}{\bfseries\sffamily\thepage}{}{\bfseries\sffamily\leftmark}
\makeoddhead{main}{\bfseries\sffamily\rightmark}{}{\bfseries\sffamily\thepage} 
\addtopsmarks{main}{}{%
  % insert "Chapter\space" & "Section\space" if desired as 4th argument:
  \createmark{main}{left}{shownumber}{}{\,\space }% 
  \createmark{main}{right}{shownumber}{}{\,\space}%
}
\makeevenfoot{main}{}{\bfseries\sffamily\thepage}{}
\makeoddfoot{main}{}{\bfseries\sffamily\thepage}{}

\renewcommand{\contentsname}{Table of Contents}

\newcommand{\frontheads}[1]{%
  \makeheadrule{headings}{\textwidth}{\normalrulethickness}
  \makeevenhead{headings}{\bfseries\sffamily\thepage}{}{\bfseries\sffamily{#1}}
  \makeoddhead{headings}{\bfseries\sffamily{#1}}{}{\bfseries\sffamily\thepage}
  \makeevenfoot{headings}{}{\bfseries\sffamily\thepage}{}
  \makeoddfoot{headings}{}{\bfseries\sffamily\thepage}{}
}
\newcommand{\backheads}[1]{%
  \makeheadrule{headings}{\textwidth}{\normalrulethickness}
  \makeevenhead{headings}{\bfseries\sffamily\thepage}{\bfseries\sffamily{#1}}{}
  \makeoddhead{headings}{}{\bfseries\sffamily}{\bfseries\sffamily\thepage}
  \makeevenfoot{headings}{}{\bfseries\sffamily\thepage}{}
  \makeoddfoot{headings}{}{\bfseries\sffamily\thepage}{}
}

\chapterstyle{default}

\usepackage{lipsum}

\begin{document}

\frontmatter

\frontheads{Table of Contents}
\tableofcontents\cleardoublepage

\frontheads{Preface}
\chapter{Preface}
\lipsum[1-9]\cleardoublepage

\pagestyle{main}  % <--- SEEMS TO BE IGNORED!
\mainmatter

\chapter{One}
\lipsum[1]

\section{A section}
\subsection{First}
\lipsum[1-7]
% Many (sub-)sections to force multi-page TOC
\subsection{Second}
\subsection{Third}\subsection{Four}\subsection{Five}\subsection{Six}
\subsection{Seven}\subsection{Eight}\subsection{Nine}
\subsection{Ten}\subsection{Eleven}\subsection{Twelve}
\subsection{Thirteen}\subsection{Fourteen}\subsection{Fifteen}
\subsection{Sixteen}\subsection{Seventeen}\subsection{Eighteen}
\subsection{Nineteen}\subsection{Twenty}\subsection{Twenty-one}
\subsection{Twenty-two}\subsection{Twenty-three}\subsection{Twenty-four}
\section{B section}\section{C section}\section{D section}
\section{E section}\section{F section}\section{G section}\section{H section}
\section{I section}\section{J section}\section{K section}\section{L section}
\section{M section}\section{N section}\section{O section}\section{P section}
\section{Q section}\section{R section}\section{S section}\section{T section}
\section{U section}\section{V section}\section{W section}\section{X section}
\section{Y section}\section{Z section}\section{AA section}\section{BB section}
\section{CC section}\section{DD section}\section{EE section}\section{FF section}
\section{GG section}\section{HH section}\section{II section}\section{JJ section}
\section{KK section}\section{LL section}\section{MM section}\section{NN section}
\section{OO section}\section{PP section}\section{QQ section}\section{RR section}
\section{SS section}\section{TT section}\section{UU section}\section{VV section}
\section{WW section}\section{XX section}\section{YY section}\section{ZZ section}

\chapter{Two}

\backmatter
\backheads{Guide to the Literature}
\chapter{Guide to the Literature}
\lipsum[1-10]

\end{document}

The wrong even- and odd-numbered page heads for the mainmatter are being printed like this:

The correct even- and odd-numbered page heads for the frontmatter (and backmatter) are printed like this:

Note: See also memoir: headers for short and detailed tables of contents

Answer 1

I'd drop the \frontheads and \backheads and define a proper main style and activate it in the preamble.

The main problem is your psmarks:

\makepsmarks{main}{%
  \createmark{chapter}{both}{shownumber}{}{\enspace} % use both not left
  \createmark{section}{right}{shownumber}{}{\enspace}
  \createplainmark{toc}{both}{\contentsname}
  \createplainmark{lof}{both}{\listfigurename}
  \createplainmark{lot}{both}{\listtablename}
  \createplainmark{bib}{both}{\bibname}
  \createplainmark{index}{both}{\indexname}
  \createplainmark{glossary}{both}{\glossaryname}
}

Then by activating this in the preamble and getting rid of your \frontheads and \backheads I seem to be getting exactly the same output as you get with those two macros

The error you made in the MWE is this:

\addtopsmarks{main}{}{%
  % insert "Chapter\space" & "Section\space" if desired as 4th argument:
  \createmark{main}{left}{shownumber}{}{\,\space }% <-- main is wrong here
  \createmark{main}{right}{shownumber}{}{\,\space}% <-- and here
}