This process is a trap, and it is one too many people accept as normal. Manually assigning references to 100-200 receipts daily, then cross-checking multiple sheets to avoid duplicates, is not spreadsheet work, it is data entry disguised as data management. The user who posted this question is not asking for a trick or a shortcut. They are asking for a way out of a system that was never designed to scale with their actual workload.
The practical reality here is that human eyes are not built for this kind of repetitive pattern matching. When you are scanning hundreds of rows across multiple sheets, looking for a single reference number you may have already assigned, your error rate climbs with every transaction. The user's struggle to "keep up with the last series" is not a personal failing. It is a design failure of the tool they are using. Traditional spreadsheets treat duplicate detection as a manual audit step, not an integrated function. That is the fundamental problem.
What this user needs is not a better formula or a clever conditional formatting rule. They need a system that understands context across sheets. An AI-native spreadsheet can look at every reference, every receipt, and every sheet simultaneously, flagging duplicates the moment they appear. It can learn the pattern of your assignment series and suggest the next unused reference before you even type it. This is not about replacing the user's judgment. It is about removing the mechanical overhead that consumes hours of focus every day, so the user can spend that time on something that actually requires their attention.
Our opinion is plain: if your tool requires you to manually hunt for duplicates across multiple sheets, then your tool is working against you. The solution is not to memorize another keyboard shortcut or build a more complex macro. It is to explore a platform that treats duplicate detection as an automated, always-on capability rather than a chore you must schedule into your day. Stop asking how to find duplicates faster. Start asking why your spreadsheet cannot do it for you.