The patentee of patent ab is different.

If Company B made the product after Company A applied for the patent, Company B will not be able to continue to produce the product after the patent of Company A takes effect (authorization announcement). Before the entry into force, B (including other members of the public) did not know the existence of this patent, and Company A did not own the patent right, so it was impossible to prevent B from producing products. However, if Company A applies for an invention patent, it can ask B to pay a reasonable royalty after the invention patent is published, but it is not mandatory.

In the absence of priority, priority refers to the retrospective relationship between two patent applications.

We assume that AB Company made the products and sold them to the public, that is to say, the products were not made in China, but began to be sold.

A's patent was applied in July 2008, but B didn't start making this product until March 2008. That is to say, before A applied for the patent, B had already started making this product, so A's patent could not affect B's making this product. If Company B doesn't want to spend time invalidating A's patent when facing a lawsuit, then Company B can claim the right of first use, and the priority is not infringing.

In fact, if we want to complete it completely, Company B can and should declare A's patent invalid, because the same product was published before A applied for a patent, so A's patent is not novel.