Expectations from p p→ t tX and p p→ b bX for missing p T distributions of electron + jet events at the SPS collider are presented and compared. Effects from extra neutrinos emitted in the events, QCD radiation off bottom quarks and UA1 calorimetric errors are included. It is shown that after all these effects are duly taken into account qualitative differences between missing p T spectra for t t and b b events essentially disappear. The remaining quantitative differences would require experimental data with very high statistics in order to be used alone to establish evidence for production of top particles.