Complex sentence: ERPA featured only referred high quality series, featuring some form of refereeing, and the AEI was designed to complement ERPA by collecting research materials on European integration which did not necessarily meet ERPA's high quality standards.
Split into simpler sentences: ERPA featured only referred high quality series, featuring some form of refereeing. The AEI was designed to complement ERPA by collecting research materials on European integration which did not necessarily meet ERPA's high quality standards.