Property history for agents: from one URL to an auditable timeline

Start with identity, not a listing ID

Every portal or agency assigns its own identifier to an appearance. Property identity should survive a changed URL, agency, description or price. It can be built from address or geographic cell, type, area, floor, year, attributes and permitted perceptual signals.

Matching is not binary truth. Every connection needs a score, reasons for and against, and a status such as proposed, reviewed, confirmed or rejected. One bad merge contaminates the entire history and CMA.

Treat every appearance as an observation

For each licensed, partner or user-submitted source, retain the source URL, source listing ID, first and last seen dates, observed price, status, core facts, capture mode and usage rights. An internal evidence record does not require republishing third-party descriptions or images.

Observations remain immutable while events are appended to the timeline: PRICE_OBSERVED, PRICE_CHANGED, STATUS_CHANGED, SOURCE_REMOVED and MATCH_CONFIRMED. The system can then reproduce what was known on any date.

Disappearance does not mean sold

A listing can disappear because it sold, rented, expired, was withdrawn, changed agency, was replaced or was blocked. SOURCE_REMOVED must not become SOLD without separate and appropriate evidence.

The interface should say “no longer observed at the source” and show the last check date. If a verified transfer appears later, it becomes a separate event with its own provenance and match probability.

Removal is an observation. Sale is a conclusion that requires additional evidence.

The timeline an agent needs

A professional view should answer quickly: how many unique appearances were found, what are the first and last observations, how many price changes occurred, which facts conflict and which match needs human review.

In a CMA, active asking observations belong to the competition set. Earlier appearances inform positioning and the owner conversation. Only suitable verified transaction records enter the closed-evidence set.

Rights, retention and the audit trail

Every source adapter needs a documented lawful basis or licence, permitted fields and purposes, cadence, attribution, retention and correction or deletion process. Public accessibility and robots allowance do not by themselves grant commercial reuse rights.

The audit trail records who confirmed a match, which rule or model version ran and what evidence was available. This makes the report reproducible and permits corrections without silently rewriting history.

Workflow from URL to report

An agent submits a URL or property facts. The system safely imports permitted fields, proposes a property identity, searches the licensed evidence store, presents possible matches and routes uncertain cases for review. It then creates the timeline, conflict ledger and CMA-ready export.

Until real feeds and sufficient historical coverage exist, the product must display coverage by source and date rather than claim “complete history”. The subscription pays for a faster, organized and auditable workflow—not for data that does not exist.

Sources and further reading

Curated primary standards, official guidance and foundational research. Source register reviewed 31 August 2026.

1. RICS — Comparable evidence in real estate valuation (2023)Selection, verification, analysis and adjustment of comparable evidence.
2. IVSC — International Valuation Standards (2025)International framework with dedicated requirements for Data & Inputs and Documentation.
3. IAAO — Standard on Mass Appraisal of Real Property (2023)Model specification, calibration, data quality and out-of-sample testing for mass appraisal.
4. Υπουργείο Εθνικής Οικονομίας και Οικονομικών — Βελτίωση παρουσίασης στοιχείων του Μητρώου Αξιών Μεταβιβάσεων Ακινήτων (Μ.Α.Μ.Α.) (2025)Official announcement on annual bulk files for published MAMA fields and their periodic update.