This discovery came about (for me) when dismantling the EF7 which was being used as a parts car and I noticed it had the 262mm brakes on it. I had been doing a comparison between ED9 and DA9 (the other knuckle in the pics)to see what, if any, dimensional differences there were between them.

No-one has been able to explain why, or where the EF8/EF9 knuckles came from or whether they were specific to those models only. I suspect when Honda was upgrading the brakes to 262's they hunted around in their parts bin and found some from another model and the difference in the steering arm didn't present a real problem to the geometry.

One of the guys who tracks an ED9 commented on a problem he had with the DA9 knuckles because of his car being extra low (the DA9's are longer from top ball joint to lower ball joint than ED9 knuckles) which pushed his UCA up too far.
He found some from a Gen 3 Prelude which he says are shorter and have improved his handling. I haven't had an opportunity to check any of them out to see if they are the ones Honda used, would love to do so.