O rsync inicia a transferência dos arquivos antes de concluir o rastreamento para ver exatamente quantos existem, para acelerar o processo geral. Isso significa que o número sobe quando está em execução.
A partir do rsync 3.1.0, isso mudou um pouco:
The output of the --progress option has changed: the string "xfer" was shortened to "xfr", and the string "to-check" was shortened to "to-chk", both designed to make room for the (by default) wider display of file size numbers without making the total line-length longer. Also, when incremental recursion is enabled, the string "ir-chk" will be used instead of "to-chk" up until the incremental-recursion scan is done, letting you know that the value to check and the total value will still be increasing as new files are found.