If it happened in dozens of labs… how the fuck does big pharma hold patents on certain drugs? The existence of a patent means the drug was developed and patente

If it happened in dozens of labs… how the fuck does big pharma hold patents on certain drugs? The existence of a patent means the drug was developed and patented by one entity. If a molecule, synthesis path, or mechanism has already been disclosed in the literature by multiple labs, then that is public prior art and it cannot be patented. Therefore, If there were dozens of other researchers coming up with the same drug the patent is legally invalid. So it seems you’re the one not making sense.