First Day Cover Postmark Date Match Validator
Compare real civil postmark and caller verified first-issue dates; matching date does not authenticate first-day use. Caller independently verifies observations, reference edition, units and applicability; not a grading-service certificate, authentication, conservation treatment, actual market price or legal/insurance entitlement.
Description
A first-day cancellation should be compared with the relevant issue date under an explicit calendar convention.
A first-day cancellation should be compared with the relevant issue date under an explicit calendar convention.1
This validator reports exact date equality and the signed postmark-to-issue interval.
When to use First Day Cover Postmark Date Match Validator
Use this tool when you need to summarize the supplied collecting records or matched observations. Prepare independently verified observations, reference edition/context, and matching units or currency basis.
How to use First Day Cover Postmark Date Match Validator and understand its results
- Prepare independently verified observations, reference edition/context, and matching units or currency basis.
- Enter postmarkDate, callerVerifiedFirstIssueDate, following the field table and calculation rules below, then run the tool.
- Read matchesCallerFirstIssueDate, signedPostmarkAfterIssueDays. For result objects, inspect the nested output fields below, including any missing evidence or selected indices.
- Correct any input issues and run again. Before using a successful result, review its units, signs, evidence coverage, and stated model or reference assumptions.
| Input field | Meaning | Value type | Requirement |
|---|---|---|---|
| postmarkDate | Postmark date | string | Required |
| callerVerifiedFirstIssueDate | Caller verified first issue date | string | Required |
Validate real YYYY-MM-DD issue and postmark dates, subtract issue day from postmark day, and return whether the signed difference is zero. A before-issue postmark gives a negative gap; differing valid dates successfully return false.
gapDays=postmarkDay−issueDay; firstDayMatches=gapDays=0 Read these symbols with the field meanings and branch or reference rules above.
| Output field | Meaning | Value type |
|---|---|---|
| matchesCallerFirstIssueDate | Matches caller first issue date | boolean |
| signedPostmarkAfterIssueDays | Signed postmark after issue days | number |
{
"input": {
"postmarkDate": "2026-01-02",
"callerVerifiedFirstIssueDate": "2026-01-02"
},
"output": {
"matchesCallerFirstIssueDate": true,
"signedPostmarkAfterIssueDays": 0
}
}Limitations and assumptions
Observations, reference edition, and applicability are independently supplied. Arithmetic and reference summaries do not provide authentication, a certified grade, or an actual market price.
Missing required fields, unknown fields, wrong types, and violated calculation rules return input issues.
Alternative or Complementary methods
For a related task, use Transit Time Postmark Interval Days Between Marks Calculator: Transit postmarks record dates at points along a postal route, allowing a calendar-day interval to be summarized. This calculator keeps the sign of the interval so reversed or inconsistent dates remain visible. For a complementary step, use Rate Period Date Bracket Finder for Postal History: A historical rate period defines the dates when a particular postal reference applies. This finder checks explicit supplied start and end dates and preserves overlapping matching records instead of choosing one silently.
References
Similar or alternative tools
- Transit Time Postmark Interval Days Between Marks Calculator
Transit postmarks record dates at points along a postal route, allowing a calendar-day interval to be summarized. This calculator keeps the sign of the interval so reversed or inconsistent dates remain visible.
- Rate Period Date Bracket Finder for Postal History
A historical rate period defines the dates when a particular postal reference applies. This finder checks explicit supplied start and end dates and preserves overlapping matching records instead of choosing one silently.