A boundary states what belongs in an analysis and what falls outside it. Dates are one boundary. Branches, product ranges, customer types and transaction states are others. Clear boundaries stop a narrow finding from being presented as a claim about the whole business.
Record the boundary before selecting the data. Also record which date field controls inclusion: order date, invoice date, payment date or delivery date. These describe different events and need not fall in the same month.
A small-business example
A wholesaler asks for August revenue. The export contains invoices raised in August, payments received in August and orders entered in August. Combining them without a rule produces a number that has no stable meaning.
For a particular operational report, the team agrees to count invoices dated within August for one branch, with credit notes shown explicitly. The bookkeeper checks whether that definition suits the intended use. The report carries the definition alongside the result.
Try this
Write a one-sentence inclusion rule for your next analysis. Then name three plausible records that should be excluded. Check records on either side of the date boundary and one cancelled or reversed transaction. These cases often expose assumptions that ordinary rows do not.
Connect the rule to Ask a better question, record dates precisely in your Data dictionary, and use Provenance to retain the export and selection details.