I recall seeing similar variations on other films at the Massive Development Chart. I believe they post a variety of times/temps from a number of contributors, who, I assume, have a huge variation in techniques, temps, agitation, enlargers, lenses, cameras, light sources, meters, metering techniques, etc. I take their info, and most other info that doesn't fit my personal conditions and techniques, as a starting point, and not much more. I figure I'm lucky if I get to within +/- 25% of the correct development time with reference material of this nature, but that's almost always much better than starting from nothing.
Lee