[Context and motivation] A key requirements consideration in software development is the system’s quality requirements. Quality is usually defined in terms of global properties for a software system, such as “reliability”, “usability” and “maintainability”. In the context of software maintenance they are particularly relevant: maintenance activities are performed to ensure software quality. [Question/problem] Recently an expanded view of RE has been emerging, wherein requirements artifacts play a role throughout a system’s lifecycle. How important are quality requirements as the lifecycle progresses? We examine two questions: whether requirements are discussed more as the software matures; secondly, whether different software projects have similar levels of interest about quality requirements. [Principal ideas/results] We use a software repository mining technique we call signifier extraction, and empirically investigate the treatment of software quality in software projects. Signifiers are keywords about quality requirements that we generate using a controlled taxonomy based on ISO9126. Using source data extracted from eight open-source software projects we extract the signifier frequencies over weekly intervals. We analyze the signifier occurrence patterns statistically and historically. [Contribution] Our results show that quality requirements are discussed differently in different projects. Furthermore, there is no correlation between project age and the importance of software quality requirements. Finally, we show that these occurrences provide a roadmap to reconstruct the historical changes of qualities as responses to external forces, such as release cycles and usability audits.