Do Multiple Referrals Actually Help for MBB Recruiting?

I’m trying to understand what happens behind the scenes when a candidate is referred at McKinsey, Bain, or BCG.

Can more than one person at the same firm refer the same candidate, or is only one referral ultimately connected to the application? If multiple employees submit referrals, does that strengthen the application, create confusion, or make no meaningful difference?

How common are referrals in the MBB applicant pool? Do most serious candidates already have one, or can a referral still meaningfully differentiate an application?

Would appreciate insight from anyone familiar with recruiting at MBB. Thanks!