You need to get BI’s that have a population of 10^6.
All the lethality calculations are acedemic and useful, but are not confirmation that you get sufficient kill. The lethality calculations assume that you are getting steam penetration, and that the steam is saturated, and a few other calculations.
So you can be challenged (by regulators) just using the lethality calculations, or using 105 BIs, when you are trying to prive 106 reduction.
We did get an audit finding on this oversight once. Our intention was to use 106 BIs, but we used the wrong ones (oops).