If the harassment counselor wishes to file anonymously, would it be acceptable to assign only a case number?

Hello. We operate a workplace harassment counseling service at a company with approximately 500 employees.
Recently, a caller requested that a record of the call be kept so that they could contact us again regarding the same matter, even though they did not wish to reveal their name and affiliation at the moment. Previously, anonymous consultations were recorded only with the date and department, but when multiple similar consultations were received, it was difficult to distinguish whether they were follow-up contacts from the same person.
We are currently reviewing a plan to assign case numbers instead of names and instruct counselors to keep the numbers, while keeping only the filing date, contact channel, key issues, whether immediate protection is required, and the next contact method in internal records. However, we are concerned about whether it is possible to verify the facts necessary to initiate an investigation or take protective measures using only the case number, and how to verify identity if the number is lost.
Is it acceptable to assign only a case number during the anonymous consultation stage? I would like to know the information that needs to be verified when the case is converted to an official report, how to separate consultation and investigation records, and how to determine the access rights and retention standards for case numbers.