(Remember that every test has its limitations - PSA, MRI, biopsy, biomarker, and yes even PET scans.)

As @jeffmarc mentions, some prostate cancers (said to be in the range of 10%-15%) are PSMA-negative (or PSMA-naive), such that the prostate cancer does not express the PSMA protein on its cell surface (or too little to be detected), in which case a PSMA PET scan will not "see" the tumors, even if other tests (like a rising PSA or biopsy) confirm the cancer is present and growing.

Also consider that prostate cancer is very heterogeneous, not just from person to person, but also sometimes within one person; some prostate cancer cells may express PSMA while others may not.

PSMA PET scans outperform the other (older) types of PET CT scans (like FDG, NaF, Choline C11, and Axumin) - just as long as the prostate cancer cells are producing enough PSMA to be detected.

In the cases when it isn’t, the older types of PET scans, ones that aren’t dependent on PSMA - like the older Axumin or Choline C11 PET scans - might be able to detect the location of the prostate cancer. (Mayo Clinic often uses the older C11 Choline PET scan for this purpose.)

For prostate cancers that may be PSMA-negative, Axumin®
(F18-Fluciclovine) is often used. (Insurance still covers it.) Axumin PET scans don’t rely on PSMA.

Axumin works by exploiting the fact that prostate cancers absorb amino acids at a much more rapid pace than normal cells. Axumin is made up of a radioactive tracer linked to an amino acid. Cancer cells absorb the amino acids more avidly than normal cells, so when Axumin is used, the radioactive tracer concentrates inside the tumor cells. Then during imaging, the areas that have a high concentration of the imaging agent signal the location of the cancer.

Just something to consider in the future if needed (which hopefully it won’t be!)