I hope I figured something out this year !
I've planted "Hardneck" Garlic for several years, planting in Oct (usually late Oct) and harvesting in July.
Some years, I've had some failure and I may have figured out why that is. When I was talking to other growers at this year's Garlic Festival, I was told that Minnesota can have some winters that start early, if the Garlic doesn't start growing in the fall, it's likely to rot in the Spring's "freeze-thaw" cycles that we often get.
So, this year, I planted in mid September. I think planting in Mid to Late Oct was just too late for my area.