According to the Sieve documentation, when using an expression like:

header :list "from" ":addrbook:personal?label=Your Contact Group"

... the matching variables will be altered. The matching variable ${0} will always contain the last email address contained in the specified list. If the list was marked with the note 1, the matching variable ${1} will contain the display name.

I would like to see at least one more address book field exposed to the script. Having the Notes field populated into ${2}, would allow more information to be passed to the filter about the contact, which could be used to better process the email. Admittedly, this is valuable to more complex filters, but someone using Sieve is already doing more complex filtering.