%%%%%%%%%%%%%%%
% central.tex %
%%%%%%%%%%%%%%%
saveContent{A}{this is content "A"}
saveContent{B}{this is content "B"}
saveContent{C}{this is content "C"}
saveContent{D}{this is content "D"}
% vdots

%%%%%%%%%%%%%%%%
% document.tex %
%%%%%%%%%%%%%%%%
documentclass{article}
input{central.tex}

useContent{A}
useContent{B}
useContent{C}

begin{document}
  displayUsableContent
end{document}

+---+  +---+  +---+  +---+
| A |  | B |  | C |  | C |
|   |  | B |  | C |  | D | % (breaking D onto its own page would be acceptable)
|(1)|  |(2)|  |(3)|  |(4)|
+---+  +---+  +---+  +---+

+---+  +---+  +---+  +---+
| A |  | B |  | C |  | D |
|   |  | B |  | C |  |   | % where is my C :(
|(1)|  |(2)|  |(3)|  |(4)|
+---+  +---+  +---+  +---+

+---+  +---+  +---+  +---+
| A |  | B |  | C |  | D |
| B |  | C |  | C |  |   | % B is broken but doesn't need to be :(
|(1)|  |(2)|  |(3)|  |(4)|
+---+  +---+  +---+  +---+

documentclass{article}
usepackage[most]{tcolorbox}
usepackage{lipsum}

tcbset{enhanced, breakable, height fixed for=all}

begin{document}
begin{tcolorbox}[height fill, title=Problem A]
lipsum[1]
end{tcolorbox}
begin{tcolorbox}[height fill, title=Problem B]
lipsum[1-3]
end{tcolorbox}
begin{tcolorbox}[title=Problem C]
lipsum[1-5]
end{tcolorbox}
begin{tcolorbox}[height fixed for=none, title=Problem D]
lipsum[1-5]
end{tcolorbox}
begin{tcolorbox}[height fill, title=Problem E]
lipsum[1]
end{tcolorbox}
end{document}