n my impression, the later ones are all supposed to be successors of the previous but within about the same chip area. The A55 is basically a refined A53 with support for DynamIQ. The point of the A510 was support for ARMv9 with SVE2, but it is wider also because people expect faster processors. To amortise the cost of the larger back-end it lost 32-bit support and there's an option to make a cluster of two share the same FP/SIMD/SVE unit and L2 cache.