Unlike "dead" languages like Latin where usage and meaning are fixed for all time, modern languages [like English] are "alive" and constantly take on new usage and forms which is why there are more words and definitions in the OED now than ever before. It is also why Latin is commonly used in legal and medical references where an exact and unchanging meaning is required.
The plural usage in this case is sound and is already widely accepted.
The plural usage in this case is sound and is already widely accepted.