You can announce the winner without announcing the tally.
As Jim Noble (courtesy ping) pointed out in his #32,
How will the states in the NPV compact define “the popular vote”?
Who would validate that enumeration? ABC News?
mmm...
The electors don’t meet until the middle of December. Disputes within states about which electors go are to be decided six days before that meeting. Plenty of time to ferret out state-by-state vote totals, as such totals are (theoretically) witnessed by multiple representatives and are not in any way secret.
Current federal law (Title 3, chapter 1, section 6 of the United States Code) requires the states to report the November popular vote numbers (the “canvas”) in what is called a “Certificate of Ascertainment.” They list the electors and the number of votes cast for each. The Congress meets in joint session to count the electoral votes reported in the Certificates of Ascertainment. You can see the Certificates of Ascertainment for all 50 states and the District of Columbia containing the official count of the popular vote at the NARA web site.