No recollection, but I got curious and found that it changed in mid-1980's. It looks like the industry standard was actually revised in 1983, but how long after that it took to adopt the change I don't know.
What I really wondered was how significant the difference would be. In one comment I found it said 50 at the powerhead would be 40 at the prop. I was surprised the difference was that much.
But I'm just reporting from google. Hopefully someone with more knowledge will chip in.