A referral tracking system is the record of an introduction after it leaves the conversation: who introduced whom, the deal that introduction became, and the fee owed for it. A spreadsheet can hold those three facts. It stops being enough when more than one person has to keep them true.
The introducer is a person on the referral, not a name typed into a notes field. When a second person introduces the same prospect, both stay on the record.
The introduction is tied to the opportunity it became, and it stays tied when that opportunity moves.
The fee is part of the same record as the deal, so what you owe is a lookup, not a reconstruction from a thread.
That is the layer next to the system you already use for customers. See how Introzy tracks a referral.
A sheet is a fine referral tracking system while one person owns it and the volume stays small. These are the points where it stops:
Skip the category labels. A referral tracking system has to keep the three records above intact:
If the sheet is still where the referrals live, get the free referral tracker and bring them across from there.
Track introductions, keep the introducer on the deal, and see the fee owed, without a second copy of the sheet.