At least at that time, there was no isolated virus available to the CDC, which can only mean the ‘virus’ was never initially isolated as numerous studies claimed to have done, including the CDC study published just the previous month.

It took me 2 minutes searching to find the answer to your confusion on this issue: https://www.bmj.com/content/371/bmj.m3925/rr-3

One essential step in method characterization is to determine the limit of detection (LoD). As this requires a quantitative readout from the assay, one needs to use a precisely quantified reference substance as calibrant, ie it needs to be known in the reference that the SARS CoV2 RNA genome is exactly present at a concentration of X copies/µl.

This statement simply means that this exactly quantified isolate is not available, but the isolate are available. The exactly quantified reference substance is available in the form of in-vitro transcribed RNA. This was used for the quantitative studies to establish the LoD.