It could be that Polaris 12 is a refreshed or rebinned Polaris 11, perhaps to fill the big performance gap between Polaris 10 and Polaris 11. Alternatively, it's also possible that Polaris 12 could be even slower than the Polaris 11 GPUs.
Linux driver files reveal there are six device IDs for Polaris 12 GPUs, which could be anything from desktop, mobile to professional GPUs.
VideoCardz also dug up some Polaris 12 benchmark results from the Ashes of the Singularity and GFX Bench databases. The Ashes of the Singularity results indicate Polaris 12 is a very slow GPU.