curl https://www.openssh.com/releasenotes.html \
     | sed -nr '/^<h3><a/s/.*OpenSSH ([0-9.]+).*\(([0-9-]+)\).*/\2\t\1/p' \
     | sort \
     | sed -r 's|([0-9]+)\.([0-9]+)\.([0-9]+)|\1.\2\3|' \
     | column -t -N 'Date,Version' > openssh.dat
  head openssh.dat

Which yields:

  gnuplot -p -e '
    set xdata time;
    set timefmt "%Y-%m-%d";
    set xlabel "Date"; set format x "%Y";
    set ylabel "Version";
    f(x) = a*x + b;
    a = 1e-10; b = -100;
    fit f(x) "openssh.dat" using 1:2 via a,b;
    set label 1 sprintf("Fit: Version = (%.3e * Date) %.3f", a ,b) at graph 0.05,0.95 left;
    plot "openssh.dat" using 1:2 with points title "Versions", f(x) with lines title "Fit"
  '

Which yields:

Note that Date are Epoch timestamps.

export VERSION="43.2"

date +%Y-%m-%d -d \
 @$(
    export m="9.55651e-09";
    export c="-6.75132";
    ## Use python for better scientific number handling 
    python -c "print(($VERSION - $c)/$m)"
 )