  This paper is a follow-up of Ref.~\cite{Ravasio:2018lzi}, where we studied
the impact of next-to-leading order calculations merged with parton shower
generators (NLO+PS) of increasing accuracy in the extraction of the top mass at
hadron colliders. Here we examined results obtained with the older
(fortran-based) shower generators Pythia6.4 and Herwig6.5. Our findings are in
line with what we found in our previous paper with the new, c++-based,
generators Pythia8.2 and Herwig7.1.
