US regulatory tooling is designed to attach source, effective-date and last-verified metadata to state or federal rules. UK regulatory tools follow the same principle for Companies House, HMRC and other official government data. Imported US sales-tax datasets retain effective-date and checksum metadata for traceability.
Primary-source principle
For regulatory calculators, official government or administering-body sources should take priority over secondary summaries. Source metadata should include the effective period and a last-verified date wherever possible.
Data freshness
Because rates and legal rules can change, SMECalculator.com should not present an old rule as current merely because it remains stored in the engine. Administrators are expected to review country-specific datasets before publication and after relevant rule changes.