But we can still talk probabilistically.
If only 20% of contractors do proper load calculations, then the odds that all three of this guy's contractors is less than 1%. And when we figure in the chance that each contractor's equipment is that variable in tonnage ratings, you must concede that your hypothesis, while certainly possible, is highly unlikely.
My experience leads me to suspect that each of those three men did a cursory walk through and then based their bids on equipment that they've put in similar looking houses.
It is for this reason that I recommend to all of these homeowners who are so fussy about manual J to simply learn to do it themselves, then compare what they got to their most trusted contractor.