  Background: Systematic literature studies (SLS) have become a core research
methodology in Evidence-based Software Engineering (EBSE). Search completeness,
ie, finding all relevant papers on the topic of interest, has been recognized
as one of the most commonly discussed validity issues of SLSs. Aim: This study
aims at raising awareness on the issues related to search string construction
and on search validation using a quasi-gold standard (QGS). Furthermore, we aim
at providing guidelines for search string validation. Method: We use a recently
completed tertiary study as a case and complement our findings with the
observations from other researchers studying and advancing EBSE. Results: We
found that the issue of assessing QGS quality has not seen much attention in
the literature, and the validation of automated searches in SLSs could be
improved. Hence, we propose to extend the current search validation approach by
the additional analysis step of the automated search validation results and
provide recommendations for the QGS construction. Conclusion: In this paper, we
report on new issues which could affect search completeness in SLSs.
Furthermore, the proposed guideline and recommendations could help researchers
implement a more reliable search strategy in their SLSs.
