In fact not as much. There is a lot of rumour about how stressing is increasing the alkaloids within cacti, but not real evidence. The only seemingly working way how to increase alkaloid content is leaving the cacti in the darkness for few months. The dormancy period might do the same, as would be indicated by my numbers.

I don't believe any other form of stressing is increasing alkaloid content, so am not planning to do any tests in that area.

The same is for the correlation of the age of the cactus and the potency. Rumours but not real evidence.
Someone says the bottom part is stronger, someone the upper part (here we have some data provided by An1cca). Maybe the growth from the same season is more potent in the upper part of the cactus, but when we are comparing two parts of the cactus from two periods divided by dormancy, the bottom part is more potent.
In worse scenario, every cactus is different and we can't generalize.

I have added sample #99 - The Koehres peruvianus grown on pereskiopsis

Interesting graph - the most subjectively bitter cactus had the lowest alkaloid content! And the second and third most potent in terms of neutralisable substances were only 0.8 on the bitterness scale.

It appears to be the case that some cacti produce a very bitter substance that is not an alkaloid, which makes me think that some kind of test for non-alkaloidal bitter substances would be useful. Unfortunately the range of non-alkaloidal bitter substances is large and diverse. My best guesses for where to start looking in this respect would be some kind of iridoid glycoside, or a diterpene.

Whatever is causing the bitterness, now it seems to me that bitterness can hardly be used as a reliable indicator of potency.
- #99 shows strong bitterness doesn't mean high alkaloid levels
- #121 shows no bitterness doesn't mean lack of alkaloids
- and yes #14 and #288 show low bitterness doesn't mean low potency. Though 4.34 and 4.07 mg/g*10 are not very high values

Maybe for some interesting levels like 1 mg/g and more there is some minimal usual bitternes but my cactuses don't reach such values, so it is just an assumption.

We have some new information regarding the correlation of bitterness and potency. This story seems to get to its (bitter) end.