Some observations -
I don't have Bob's books so I can't comment on their content
a sample load sheet for Echo, which lists the Basic Empty Weight (BEW) as 1992 kg. BEW is whatever the originating weight control officer (WCO) wants it to be. Hence, for it to make sense, it has to be defined somewhere. The end user cannot just make up the BEW configuration.
it states "Empty Weight from flight manual" as 1970 kg. EW is a little more tightly controlled. The starting point definition is given in CAO 100.7 - see
www.legislation.gov.au/Details/F2018C00475 There is some wriggle room so, again, the EW has to be defined to make a great deal of sense. This should occur on the load data sheet or in the weight and balance pages of the POH.
Are we not talking about the same Echo Aircraft? Each individual aircraft will have its own specific declared empty weight and CG data. This will have been determined either by weighing or calculation and will change periodically.
they will still be individually weighed Generally but not, necessarily the case. Often we run the data via calculations based on previous data and configuration change data.
which is different to Zero Fuel Weight (ZFW) EW will figure in the calculation of ZFW but, apart from that, the two are not related.
gross operating weight This could mean anything but normally would be read to mean the aircraft loaded gross weight ready for operations.
"loaded for takeoff" This will mean whatever the writer intends. However, one probably would interpret it to mean something along the lines of the gross weight at the start of the takeoff run.
a lot of questions referred to operating weight Again, the term should be defined in context otherwise it can mean whatever the writer wants it to mean.
the seats *have been removed* The question (or the empty weight data) should have defined what seating configuration was included in the EW. Then one takes it from there.