Essentially, the only rule is that are no rules. This wonderful material that we work with is too diverse in its density, moisture content and grain pattern to ever adhere to a rule that we may choose to write. However, there are guidelines!
The 10% concept is a good guideline, but only experience of working a wide variety of timbers will give you the knowledge that you need to estimate the degree of movement that is likely. Straight grained pieces of timber from the bole of a tall, straight tree such as ash, will probably move less than 10%, whilst a crotch of an apple tree might well move by 20%. The moisture content is another factor, as is the species that you are using and, perhaps most importantly, the way in which the bowl is orientated compared to the grain (side-grain bowl, end grain etc).
I for one would be disinclined to put my name to any entry in a list/table/database when there are so many variables to consider.
Meanwhile, my nest suggestion would be to err on the side of caution and do your best to control the drying process.
Les
Les