All memory configs have 1M in $00c0.0000 space, where the A500 has it's trapdoor memory. This is the memory chunk that makes some A500 software work (admitted, it's bad software that has memory addresses hardcoded, but the A500+trapdoor expansion was *very* popuar).
The 17M and 33M figures are also explained by that.
The 63M figure is a result of the reserved Maprom memory. 64M physical mem minus 1M reserved for Maprom is 63M fastmem total. The highest mem config has 62M fastmem in a single chunk.