You’re not wrong, the same tests used 50 years ago (if they existed) would have shown the same results.
The flaw(feature?) is that they use a PCR test at all to identify a specific something from non specific potential somethings. Doesn’t matter what they are testing for, they can find “it” with enough cycles of a PCR test. Just keep breaking the sample into smaller and smaller pieces and as long as they can get enough broken pieces of stuff that “could” have been assembled (but obviously wasn’t) into the specific something they want, then they point to that as a “positive” result for whatever the PCR is looking for.