could have something to do with the actual block 1. the psx memory card is actually 16 blocks of 8KBs apiece (128KBs altogether). the first block is a toc that contains save names and information while the other 15 blocks are the actual saves.
edit: if you ever want to hex something in, look for SC+0x2000 hex length equals 8,192 bytes (the size of one block and the beginning of the block as well). to my knowledge, the saves themselves don't identify themselves without the toc, so there's no file name. if you convert a save to say I think mcr, the name will be in the header, since there will be no block 1 with it.