Call for tenders' details

Study on Sustainability Ratings and Research
Contracting authority:
European Commission, DG for Internal Market, Industry, Entrepreneurship and SMEs...
TED publication date:
Time limit for receipt of tenders:
English (en)
Question details
How to evidence in-house work (via the certificate of satisfactory execution)?
The member of our project team with 'capacity to provide legal analysis...' wishes to evidence suitability for the work by reference to five years working in-house. Your Call for Tenders requires as evidence 3 projects or studies and supply a 'Certificate of Satisfactory Execution' for the most important one. The Certificate of Satisfactory Execution form however, appears to be much more designed for people working on a contract / project basis and makes little sense for someone who has been working in-house. Can in-house work serve as evidence and if yes, how?
The 3 reference projects should be projects/studies/publications that the tenderer (or tenderers in case of a joint bid) has executed for third parties (public or private) in the past 5 years. In-house work for an authority that is not even a tenderer for this call for tenders cannot be accepted as reference.