My source was Appendix B of a book (which I had been led to believe was out of print) by Graham Robson. I had the figures verified (as best they could) by Hethel.
The book is 'Lotus Since the 70s - Volume 1: Elite, Eclat, Excel and Elan' first published in February 1993 (pre-S2 production, I'm afraid), ISBN No 0-947981-70-5. You may well have seen it and dismissed it as too generic a publication to bother with - I did, several times. But, there's one left here:
http://www.amazon.co.uk/Lotus-Since-70s ... 29?ie=UTF8
...and PM (01527-835656) also have a copy in their parts department.
On first opening the book I went straight to the Elan section, of course. There appeared to be nothing in there that hadn't been stated in the Mark Hughes bible, but then I saw the Appendices, and Eureka, figures were there that I had never seen before. I'm sure someone will pipe up that they've got the book, but maybe they hadn't realised the importance of the figures included therein, with which I started this thread. Maybe the Appendices are a later addition to the earlier editions.
I think you'll guess that I haven't been as excited about a publication since I stumbled across the Training Notes that we now have, available to all members, in the 'Manuals' section.
What can we do with these figures/what do they prove though?
Well, on their own, not much I suppose but, my intention (if possible) is to super-impose the VINs and various changes/improvements which have taken place throughout the production run on to these figures - headlights from opera to pods, addition of hood restraint belt, heater positions increased from four to six, windscreen washer return valve moved from boot to under-bonnet etc.
I don't (as yet) know what it'll prove but it should give us all a deeper insight and appreciation into the development of our cars...maybe.
Sy