It should be noted that the last word is "partially" a checksum... the way the seed is "broken up" is into 11bits chunks... 11 bits = 2048... hence 2048 words.

As per BIP39 (https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki#generating-the-mnemonic), you start with Entropy which is 128 to 256 bits... and divide that by 32 to get checksum length... in the case of the Ledger, they use 256 bits... so checksum length is only 8 bits... but the last word is 11 bits of info... so it's actually partially data/partially checksum.

This is why, even with just the last word missing there are still multiple "valid" combinations... as (for a 24 word mnemonic) the last word will have 3 bits at the beginning which are data... and generate up to 8 different values which will generate 8 different words.