Intel notified its customers that the Celeron M 520 will be transitioned from a Merom B2 stepping core to a new Merom-L core with A stepping on the first of June.
The only change for customers is a different CPUID which requires a BIOS update along with a microcode update in order to support the CPU correctly. Besides Intel notes that "Merom-L A stepping material has minor die size decrease due to manufacturing optimizations to
increase product availability".
As the PCN only mentions a minor die size decrease it remains open whether Intel only reduced the L2 cache down to 1MB or also managed to cut off one of the two CPU cores. My bet is on L2 Cache only, as it explicitly mentions "minor" and the CPU cores in Core-based CPUs are linked kinda tightly so it would have required some sort of redesign of the chip.