Theoretical sorting of stable and synthesizable "missing compounds" from those that are unstable is a crucial step in the discovery of previously unknown functional materials. This active research area often involves high throughput (HT) examination of the total energy of a given compound in a list of candidate formal structure types (FSTs), searching for those with the lowest energy within that list. While it is well appreciated that local relaxation methods based on a fixed list of structure types can lead to inaccurate geometries, this approach is widely used in HT studies because it produces answers faster than global optimization methods (that vary lattice vectors and atomic positions without local restrictions). We find, however a different failure mode of the HT protocol: specific crystallographic classes of formal structure types correspond each to a series of chemically distinct "daughter structure types" (DSTs) that have the same space group, but posses totally different local bonding configurations, including coordination types.Failure to include such DSTs in the fixed list of examined candidate structures used in contemporary high throughput approaches can lead to qualitative misidentification of the stable bonding pattern, not just quantitative inaccuracies. In this work we (i) clarify the understanding of the general DST-FST relationship, thus improving current discovery HT approaches, (ii) illustrate this failure mode for RbCuS and RbCuSe (a newly predicted compound) by developing a synthesis method and accelerated crystal structure determination and, (iii) apply the genetic-algorithm based Global Space Group Optimization (GSGO) approach which is not vulnerable to the failure-mode of HT searches of fixed lists, demonstrating a correct identification of the stable DST. The broad impact of items (i)-(iii) lies in the demonstrated understanding of a new strategy-use HT as preliminary broad screening, followed by unbiased GSGO of the final candidates.2