One guest, four records: the duplicate problem nobody budgets for

The same guest books once through an OTA alias, once by phone, once through your site with a different email, and once as part of a group booking made by a colleague.

In your data that is four people, each with a fraction of the value and none of them qualifying for a level. The guest concludes the programme does not work and stops paying attention.

Automatic matching should be conservative: verified email, verified phone and the PMS guest ID. Anything less certain should be a suggestion, not an action.

Merging must keep both histories. A merge that loses stay records will be discovered months later by an angry regular.

Review suggestions monthly. It takes ten minutes and it is the highest-value administrative task in any loyalty programme.