Of course I've been up all night! Not because of caffeine, it was insomnia. I couldn't stop thinking about coffee.
We have been playing that you can always mark off things in the start column. From the translated rules in another thread here:
Crosses must be horizontally or vertically adjacent to at least one already ticked box or set starting in the Start column. Box that touch only diagonally, do not count as adjacent.
It isn't worded well, but I take the second option to mean that you can tick a box that isn't adjacent to another ticked box as long as it's in the start column.