The cost that never appears on an invoice
Entering the same information into two systems shows up on no balance sheet, yet it is paid every month. It is paid in the hours someone spends copying between them, in typing errors that surface three weeks later, and in meetings that open by arguing which of the two numbers is correct.
The most expensive part is not the entry work: it is the distrust. Once a team learns a system might be stale, they stop consulting it and go back to asking. The system is still there, but it no longer supports decisions.
How to spot duplicate entry
It is not always obvious, because the team has normalised it. Three questions usually surface it. Is there data someone moves between systems by hand, even once a week? Is there a spreadsheet that "is the right one" despite an official system? Does someone have to message the team to say they updated something?
If any answer is yes, there is duplicate entry. And where there is duplicate entry there will eventually be two versions of the same figure.
Why "being careful" does not fix it
The usual reaction is procedural: define who enters what and in which order. It holds for a few weeks, until someone is on leave, work peaks, or a new person joins.
A process that depends on nobody making a mistake is not a process: it is a bet. The only stable fix is for the data to travel on its own, with a single place where it is authoritative.
Integrating does not always mean replacing
Here is the good news. If the system you already use handles 80% of the work, you do not need to change it. What is usually missing is the bridge: the web order appearing in your management system, the stock deducted in the warehouse showing up in the catalogue.
That bridge is built on what already exists and typically costs a fraction of replacing the whole tool. The team also has nothing new to learn, which is where most implementations fail.
Do not start with the tool. Start with the friction and the outcome you want to change.