To be precise: "Mehr Nastaliq Bold" is not a traditional style in classical Nastaliq calligraphy (which normally lacks bold weights). However, a few modern digital fonts (e.g., Mehr Nastaliq by Softview, or Mehr Nastaliq in some Urdu publishing suites) do include a bold variant for emphasis in digital typography.
I understand you're looking for a paper or scholarly investigation into the weight or style of Mehr Nastaliq — a famous calligraphic font for Persian, Urdu, and Arabic scripts. mehr nastaleeq bold