Requirements for proficiency testing / ILC and repeatability & repeatability

I assume from your question that you are referring to the initial formal assessment for a laboratory being assessed for accreditation for the first time. If you are referring to a requested voluntary pre-assessment by the accreditation body, prior to the initial assessment, the purpose is to identify gaps ahead of the initial assessment, so the same requirements must be met; however the purpose is to identify issues to address before the formal assessment (without formal nonconformances raised, that would have to be cleared in a specified time).

To clarify, the route to ISO 17025 accreditation by an accreditation body starts with implementation of the processes, procedures and controls by the laboratory to meet the requirements and address risks. This includes knowing the requirements of the accreditation body, which should be a signatory member of ILAC (the international organisation for accreditation bodies). This means that their requirements must be in line with ILAC policies, requirements and guidelines. The policy document ILAC-P9:06/2014 ILAC Policy for Participation in Proficiency Testing Activities is applicable to your question.

Implementation includes method validation for all the tests that the laboratory will be accredited for (will appear on the accreditation certificate) of which repeatability (precision) is one of the performance parameters. The method validations must be completed and submitted by the laboratory, typically on application. Furthermore, for each test to be accredited, laboratory processes must be in place to ensure the validity of results (clause 7.7) which includes monitoring and evaluating longer term internal quality control data (intermediate precision) for typically a few months; as well as enrolment and participation in a proficiency testing program where  a 4 to 5 year plan is usually required.

I suggest your obtain the method validation, proficiency testing and other relevant policy and requirement documents from your selected accreditation body.

The ILAC Policy documents are available at https://ilac.org/publications-and-resources/ilac-policy-series/

Have a look at the response to a question on Procedures for validation and verification of methods at https://community.advisera.com/topic/procedures-for-validation-and-verification-of-methods/

The ISO 17025 toolkit at https://advisera.com/17025academy/iso-17025-documentation-toolkit/ includes the procedure for validation and verification of methods, named Test and Calibration Method Procedure and the Quality Assurance Procedure.  The procedures are also available separately at https://advisera.com/17025academy/documentation/test-and-calibration-method-procedure/ and https://advisera.com/17025academy/documentation/quality-assurance-procedure/