Bill Gunston encyclopedias

[steelpillow]

I want to look up some ancient history in Bill Gunston's Encyclopedia of Aero Engines and his Encyclopedia of Aircraft Manufacturers. Older editions seem to sell for a lot less than more recent ones. Does anyone know whether he just updates them with current stuff for each new edition, maybe cutting back on less notable old stuff to make room, or whether he adds to the older stuff and improves it each time round? In other words, should I go for a newer edition with his latest research, or might an older edition actually be better for the historic material?

Edited June 26, 2014 by steelpillow

[Shar2]

I'd go for the newer ones as they will have been updated, but, since he died last year there won't be any more.