$NYTV represents the total volume of "New York" shares traded on the NYSE's system in New York itself.

$NYA's volume value is the total volume of all "composite" shares traded in New York AND on the regional exchanges like Chicago, Philadelphia, Boston, etc.

$NYTV's value corresponds to the Volume data reported by the Wall Street Journal.
$NYA's volume value corresponds to the Volume data reported by the NYSE website.

The volume for $NYA should always be larger than $NYTV because it draws from a larger collection of stocks and exchanges.

$NYTV is reported in "millions of shares" while $NYA is reported in "individual shares".