And if you ask EVERY SINGLE WOMAN what they do with their t.p. You'll get the same answer, "It's not MINE. I would NEVER leave it." And yet, magically, there it is... It's a mystery.
There are some 350-400,000 people who receive the compostelas each year. We know that many walk without acquiring the certificate at the end, but it's a good benchmark for a sense of how many are out there.
@Kathar1na probably has the most recent percentage by gender, but I recall it was about 40% women. So, let's say a minimum of 140,000 women on the trail... many, many of whom will be older, will have had children (which often changes bladder holding capacity).... so, let's say that 1/3 are dealing with that, and they have to pee a few times a day, and they just haven't thought about it, haven't been educated about it. 50,000 women, and who knows how many would fall into the "don't know/don't care" group, but you can see how it would quickly result in thousands of "deposits".
I see hundreds of deposits in the last days of the Frances, from Sarria onward... remarkable less frequent earlier on.
Confirmation bias can lead to those of us who see dozens of deposits per day asserting things like "It's everywhere! by the ton! Must be thousands!"
Yes, probably thousands over the course of the season... but actually not that much at any given time... (similar to how the busiest trail still falls quiet at particular times of day).
In other words, it is not common practice; it is accumulated practice... and that shows us how very important it is to prevent even practices that are not that common.
BUT -- the suggestion that people are lying about it not being theirs is rather off the plot. The statistical probability is that you are not going to meet in the thousands upon thousands of women, the relatively small number who are dropping their tissues.
Most men are not sperm donors, but somehow there can be 346 offspring of a single donor. In some parts of the world you can easily meet so many half-siblings of a single donor that it could present a real hazard. That does not mean that the man who tells you he would never donate is lying.