In terms of the EU impact assessment, I suppose the idea is to look at what is presently in place, to then see what areas will change significantly and then to try and extrapolate from that the likely outcomes - eg will manufacturing, fisheries, farming, academia, research and development, public services, etc, etc, etc., be likely to benefit or suffer as a result of leaving the EU/single market?
Surely, such assessments are carried out - admittedly on a much smaller scale - by most people when making major decisions. When contemplating a move to another area, (wise) people assess a number of things eg: commuting time and cost/local rates of pay, number and quality of schools/hospitals, etc., to try and work out how their lives are likely to be differently impacted if they choose to move to the area and how some possible negative effects could be compensated for.
My understanding is that it was originally stated that detailed impact assessments had been done but that it now transpires that no, or no meaningful, assessments were made. If these assessments are so pointless, why initially lie about having done them?