We're using the attiny2313a, and have been for some time. All works. AVR studio project file still showed attiny2313, aka 2323(v) which was clearly not a problem, because the device continued to work.
If I tell AVR studio / GCC that I'm using the attiny2313a, the code grows by 4 bytes, as expected: space is reserved in the vectors for two new (unused) interrupt vectors. This is not a problem: the code size grows from 2040 to 2044 (out of 2048). (And the last 4 bytes of a program are always unused junk inserted by GCC anyway.)
But it doesn't work. The device is unresponsive to normal inputs.
Does anyone know what might be going wrong? The listing looks identical, just shifted down 4 bytes, so I'm thinking I don't understand something.
[I hate the graphic design of avrfreaks]