he page counter does not increase in the first iteration an PDf inclusion but seems to work properly after that. Have attached a sample file (69K) that will serve to show the problem—at least, on my machine.

\starttext

\setupexternalfigures[location=default]
\setuplayer[preset=middlebottom, method=overlay]{}

\setcounter[userpage][101]
\noheaderandfooterlines

\getfiguredimensions[HannahBW.pdf]

\dorecurse{\noffigurepages}
   {\vbox to \paperheight 
       {\vskip-\dimexpr\headerheight+\headerdistance+\topspace\relax
        \hbox to \hsize
         {\hskip-\backspace
\layeredtext[]
[boffset=3pc]
{\red\userpagenumber}
{\externalfigure[HannahBW.pdf][page=#1]}%
          \hss}%
     \vss}
  }
\dorecurse{\noffigurepages}
   {\vbox to \paperheight 
       {\vskip-\dimexpr\headerheight+\headerdistance+\topspace\relax
        \hbox to \hsize
         {\hskip-\backspace
\layeredtext[]
[boffset=3pc]
{\red\userpagenumber}
{\externalfigure[HannahBW.pdf][page=#1]}%
          \hss}%
     \vss}
  }

\stoptext