Different Temp Range, Same Yeast, Different Brand?

[Argentum]

Like most folks, by choice or necessity I've occasionally substituted yeast in a recipe, like Wyeast 1056 for WLP 001. They're both Sierra Nevada and universally considered substitutes for one another. And yet WLP 001 lists a very different temp range for its yeast (68-73) than Wyeast 1056 (60-72). What gives? Are they the same or not? FWIW, Imperial Flagship also gives its range as 60-72.

 

[cswis86]

White Labs seems to list the "optimum" fermentation temperature whereas Wyeast lists the upper and lower limits. Wyeast always seems to list very wide ranges. They were both originally sourced from the same yeast but I'm sure there is some slight variation between them since they are propagated at different labs.