For the proposed split in Swainson's Thrush, it is a pity that my fairly detailed vocal analysis was not picked up.
It shows that there is a small but consistent continent-wide difference in the song, and a major difference in alarm call.
It was initially received with some scepticism by American birders, but after some checks it has been generally accepted and it even led Pieplow in his book on voices of Western North American birds (2019) to highlight the vocal differences by treating them on two different pages. Also this published reference was not included in the proposal.
Given that in another proposal in the same batch (on the graysoni taxon), Van Remsen states that in Thrushes 'vocalizations are the standard by which allotaxa are evaluated', this seems like an important omission...
Terry Chesser is the current committee Chair - I believe you can contact him if you believe more information should be considered with the proposal (and I believe others have done this as recently as last year): https://americanornithology.org/nacc/guidelines-for-submitting-a-proposal/