Multiple citations of the same reference, each time with a different page number

Question

Problem description:

1. I cite the same references multiple times;
2. each time they are cited, different page numbers are provided;
3. the page numbers are being shown together with the citation, on the article text body;
4. I'm being required to somehow make them appear not on the article text body, but instead on the references section.

What I'm doing (code):

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. \cite[pages 4 and 5]{Fonseca2020} \cite[page 16]{Silva2006}. Ut enim ad minim veniam, \cite[page 40]{Moreira2010} quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. \cite[pages 136 to 138]{Freitas2019} Excepteur sint occaecat cupidatat non proident, \cite[page 10]{Cunha2019} sunt in culpa qui officia deserunt mollit anim id est laborum.

What I'm getting:

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. [1, pages 4 and 5] [2, page 16]. Ut enim ad minim veniam, [3, page 40] quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. [4, pages 136 to 138] Excepteur sint occaecat cupidatat non proident, [5, page 10] sunt in culpa qui officia deserunt mollit anim id est laborum.

References:

1. Fonseca. "Title". (2020).
2. Silva. "Title". (2006).
3. Moreira. "Title". (2010).
4. Freitas. "Title". (2019).
5. Cunha. "Title". (2019).

What I need to get instead, somehow:

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. [1a] [2a]. Ut enim ad minim veniam, [3a] quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. [4a] Excepteur sint occaecat cupidatat non proident, [5a] sunt in culpa qui officia deserunt mollit anim id est laborum.

References:

1. Fonseca. "Title". (2020). a: pages 4 and 5, b: ..., c: ...
2. Silva. "Title". (2006). a: page 16, b: ..., c: ...
3. Moreira. "Title". (2010). a: page 40, b: ..., c: ...
4. Freitas. "Title". (2019). a: pages 136 to 138, b: ..., c: ...
5. Cunha. "Title". (2019). a: page 10, b: ..., c: ...

Question: how do I get the expected result exemplified above?

Same question as:

1. 2012 - Bibtex references, citing from same reference but different page
2. 2014 - Citing multiple chapters in the same book under the same reference number

The above pointed questions did not receive adequate answers that solves my problem.

Answer 1

Combining ideas from Customize backref similar to Wikipedia and Citation Page Numbers in Bibliography I'd like to suggest

\documentclass[british]{article}
\usepackage[T1]{fontenc}
\usepackage{babel}
\usepackage{csquotes}
\usepackage{hyperref}

\usepackage[style=numeric, backend=biber]{biblatex}

\renewbibmacro{postnote}{}

\makeatletter
\DeclareFieldFormat{bibhypertarget}{%
  \bibhypertarget{cbx:instcount:\the\value{instcount}}{#1}}

\def\abx@aux@pnbackref#1#2#3#4{%
  \listcsgadd{cbx@pnbackref@#1@#2}{#3}%
  \csgdef{cbx@pnbackref@postnote@#1@#2@#3}{#4}}

\def\blx@addpnbackref#1#2{%
  \if@filesw
    \protected@write\@mainaux{}{%
      \string\abx@aux@pnbackref
        {\the\c@refsection}{#1}{\the\value{instcount}}
        {\detokenize{#2}}}%
    \fi}

\def\blx@addpnbackref@helper#1{\blx@addpnbackref{\thefield{entrykey}}{#1}}

\def\blx@instcount@label{%
  \label{cbx@instcount@\the\value{instcount}}}

\AtEveryCitekey{%
  \iffieldundef{postnote}
    {}
    {\expandafter\blx@addpnbackref@helper\expandafter{\abx@field@postnote}%
     \ifcsundef{cbx@pnbackref@count@\the\c@refsection @\abx@field@entrykey}
       {\csgdef{cbx@pnbackref@count@\the\c@refsection @\abx@field@entrykey}{1}}
       {\csnumgdef{cbx@pnbackref@count@\the\c@refsection @\abx@field@entrykey}{%
          \csuse{cbx@pnbackref@count@\the\c@refsection @\abx@field@entrykey}+1}}}%
  \blx@instcount@label
}

\newcommand*{\pnbackref@prnt@pn}[2]{%
  \DeclareFieldFormat{bibhypertarget}{\bibhyperlink{cbx:instcount:#2}{##1}}%
  \printtext[bibhypertarget]{%
    \printtext{\alph{backrefitemcount}}%
    \setunit{\addcolon\space}%
    \printtext[postnote]{#1}}}

\newbibmacro*{pnbackref:item}[1]{%
  \ifcsvoid{cbx@pnbackref@postnote@\the\c@refsection @\thefield{entrykey}@#1}
    {}
    {\stepcounter{backrefitemcount}%
     \letcs\cbx@tempa{cbx@pnbackref@postnote@\the\c@refsection @\thefield{entrykey}@#1}%
     \expandafter\pnbackref@prnt@pn\expandafter{\cbx@tempa}{#1}%
     \setunit{\addcomma\space}}}

\newcounter{backrefitemcount}
\newbibmacro*{pnbackref}{%
  \ifcsundef{cbx@pnbackref@\the\c@refsection @\thefield{entrykey}}
    {}
    {\setcounter{backrefitemcount}{0}%
     \forlistcsloop{\usebibmacro{pnbackref:item}}
       {cbx@pnbackref@\the\c@refsection @\thefield{entrykey}}}}

\renewbibmacro*{pageref}{\usebibmacro{pnbackref}}


\renewcommand*{\bibpagerefpunct}{\addperiod\space}

\renewbibmacro*{cite}{%
  \printtext[bibhypertarget]{%
    \printtext[bibhyperref]{%
      \printfield{labelprefix}%
      \printfield{labelnumber}%
      \ifbool{bbx:subentry}
        {\printfield{entrysetcount}}
        {}%
      \iffieldundef{postnote}
        {}
        {\printtext{%
           \mknumalph{%
             \csuse{cbx@pnbackref@count@\the\c@refsection @\abx@field@entrykey}}}}}}}
\makeatother

\addbibresource{biblatex-examples.bib}


\begin{document}
Lorem~\autocite[380]{sigfridsson}
ipsum~\autocite[12-14]{worman}
dolor~\autocite{nussbaum}
sit~\autocite[381]{sigfridsson}
amet~\autocite[382]{sigfridsson}.

\clearpage

Lorem~\autocite[27-30]{geer}
ipsum~\autocite[\textbf{ä}]{worman}
dolor~\autocite[34]{pines}
sit~\autocite[382]{sigfridsson}
amet~\autocite[383]{sigfridsson}.

Dolor~\autocite[380-381]{worman}

\printbibliography
\end{document}

The code will require sufficient LaTeX reruns since the postnote is passed through the .aux file. (But I didn't build in any additional tests to check if a rerun is necessary, so you will have to make sure to run LaTeX the appropriate number of times after you change anything about the citations.)