indeterminate, undetermined

Indeterminate or indeterminate means impossible to settle or decide; not fixed, evaluated, or stipulated; having no definite end [of a jail sentence]--
We need a set of definite rules, not an indeterminate set of expectations.
We can't sign this contract because the conditions of the sale are indeterminate.
The judge has ordered an indeterminate prison sentence; he won't be released until he agrees to cooperate.

Undetermined or undetermined means not yet decided or settled; not yet established--
The cause of death was reported as undetermined, but we believe it was murder.
His fate as yet undetermined, he anxiously awaited the test results.

Now that you know that, you can say--
"The number of persons involved remains undetermined; they milled about as an indeterminate mob."