Presumably it must be logical that the more people know a secret, the less likely it will stay a secret (in the general case). Some organizations have only one level of secrecy (i.e. confidential). This is used for everything from secrets that 3 people should know, to secrets that 30,000 people should know. In the latter case, the secret is highly likely to stray outside the group.
Wouldn’t it make sense to indicate these differently? Increasingly the bureaucracy attached to such things isn’t a good thing to be doing, but surely we should also admit to ourselves that there is a practical difference between the two - perhaps to the extent of keeping fewer things secret?
Google didn’t turn up any obvious research in this area, but I’m sure there must be some.