sportsfan,
As you say, it is a little more complicated than that.
Firstly, the existing law already deals with unused visa numbers in a FY. Since they are allocated to the other half of EB/FB the next FY, they can't be said to be wasted.
Secondly, because of the existing law, any calculation would have to calculate the "net" wastage - i.e. unused but never came back to EB either via the existing law or through previous recapture legislation.
130k EB visas (from FY1999/FY2000) were recaptured as part of AC21 (this
document outlines when they were recaptured) and a further 50k EB visas were recaptured for use by Schedule A workers in a 2005 Bill.
Recapture proposals have always talked about recapture from FY1992 onwards. From then to date, about 399k visas were unused in EB. This includes the recapture of the 130k in FY2002, FY2005 and FY2007.
It does not count the 50k recaptured for Schedule A, so the figure available reduces to 349k.
In the same period, EB has received a further 289k extra numbers from FB. That would leave a net figure of around 60k (± 5k) that were unused but have never come back to EB through the existing mechanisms.
FB would benefit more, since many of the "unused" visas allotted to them did not increase the actual allocation FB received (due to the much more complex calculation of the FB allocation). That is not a consideration for EB - they receive the full amount from FB.