Those questions would not have mattered, since they would have been using simple but very accurate max/min mercury thermometers of the kind still used by gardeners in greenhouses. These have pins sealed into the u-shaped glass tube which are pushed by the two extremities of the mercury column. The pins stay at the maximum and minimum positions reached until reset by a magnet after a reading has been taken.
This would give a measurement of the coldest temperature reached in that sounding: but of course the coldest temperature would not necessarily be at the greatest depth. To check that would need repeated soundings at the same location, but at progressively reducing depths. Which, knowing the thoroughness of Victorian scientists, I've little doubt they did. I'd be wary, too, of underestimating the accuracy of Victorian scientific instruments.
Great answer, much of it brand new to me.
Thank you.
I’m not familiar with that type of thermometer but
I do know that Nansen bottles for taking water samples
at depth weren’t invented until 1910. Assuming they
could be used to maintain a temp until retrieved
at the surface.