Radio Shack emerged after Tandy bought Allied Electronics and with it their tape production. They produced tapes under the Realistic brand, and offered Low Noise, Supertape and Supertape Gold from their own production. Concertape was a budget brand sourced from multiple vendors, primarily from Ampex or Audio Magnetics. Supertape Gold was allegedly sourced from Memorex for a short time after they bought the company. Later Radio Shack branded tape was sourced from Ampex / Quantegy.
In general, their tape quality is mixed, although their own branded tapes seem to hold up well, even if they were never known at the time for their quality. The tape sourced for Concertape from Ampex (in the form of Shamrock 031 or 041) is from reject formulations sold in the 1800 ft. lengths. Other lengths may have been from different vendors at different times.
To help archivists, our research is still ongoing to determine the quality and sourcing of these tapes, and we will provide updates as we learn more.