Two different questions
A reference exchange rate helps answer a benchmarking question: what is the indicative value of one currency in another at a particular observation time? A transfer quote answers a transaction question: under specified conditions, how much will a particular recipient receive? Neither should silently stand in for the other.
Make the transaction reproducible
Record the amount, currency pair, origin and destination markets, funding and payout methods, quote time and known fees. Distinguish a fixed fee from an amount-dependent fee, and distinguish known recipient deductions from an unverified assumption. When a component is absent, preserve that absence rather than replacing it with a convenient default.
Use uncertainty in the interface
The interface should state whether a value is a reference observation, an indicative comparison or a provider-confirmed quote. If an observation has expired, its historical value can still be useful, but it must not be labelled current. A missing timestamp is not fixed by substituting the time at which the page was opened.
A publication rule
Before publishing a comparison, ask whether the source permits the intended use, whether the observations describe equivalent transactions and whether the cost components are complete enough for the intended conclusion. If any answer is unknown, display that limitation or withhold the comparison.