For the record: There is no indication whatsoever that pilgrims brought stones from home and left them at the Cruz de Ferro in earlier centuries.
There is written documentation that local travellers, especially seasonal workers who travelled for work from their homes in Galicia to the fields of Castilla y Leon stopped there to pray for a safe return home and threw a stone on the pile (19th and 20th century). This is why some Spanish pilgrims know of a tradition of picking up a stone and throwing it over their shoulder, with their backs turned to the heap of stones.
IOW, not everybody is familiar with a modern narrative that you are familiar with because you watched the movie and read it in your guidebook or on blogs on the internet.
It is the first time that I read that people leave ashes, i.e. human remains there - or at least believe that this is done.
I do understand how meaningful the Cruz de Ferro narrative and experience can be but there is an increasing tendency to assign a sacralisation to this heap of stones that many others are simply not aware of.
In my humble opinion, it would be better if there were only plain stones there and nothing else. It would certainly decrease the interest in climbing around there and looking at what others have left.