Does adding "all" in front of a singular collective noun like "staff" make it plural?

I know that "staff" is a singular collective noun. One of my clients is using the sentence, "All staff are responsible for exercising good judgment." I have edited this as incorrect because to me it needs to be "staff members" to be plural. Otherwise, it would read like, "All committee are responsible for exercising good judgment." Am I correct that using "all committee" this way is incorrect?

Solution 1:

Staff can be singular or plural. In the collective sense of the body of people working for an organisation, it is a singular collective noun (although there is some variation in how people handle singular collective nouns, that isn't what the question is about).

But Merriam-Webster also lets you use staff as a plural noun meaning members of staff (e.g. "employs three full-time staff"), so "all staff" could be a plural expression. It would be odd to use staff in this sense in the singular to mean a single person, but using it for more than one employee is fine. In such a case it will take a plural verb. Hence: "All staff are responsible for exercising good judgment."