My 2¢ not that it matters. To me a generation is how many times the yeast went through the stress to ferment a beer. Fermentation stresses and subsequent harvesting method may have more of an affect, if any, on the yeast more than fermenting a starter wort.
The yeast propagated with a new pack of yeast and the over build harvested from the starter is generation 1. Yeast harvested from a fermented beer is generation 2. When this yeast is harvested from another fermented beer it is generation 3.
I have so much harvested yeast that I've given up trying to track generations. I'll rebuild a 4 month, or so, old yeast If I have only one container of that yeast strain. I'll then store this yeast from the fresh starter in two containers in case one shows infection.