As of yesterday evening, the board had canvassed the 10 counties in the 20th and discovered that 10,055 absentee ballots had been issued by seven counties and 5,906 had been returned.
That number could go up, as three counties haven't provided their numbers. Absentee ballots must be received by April 7, but the ballots sent in by overseas/federal/military voters (recall that there was a fight over those) can arrive by April 13 and still be counted.
Of the 10,055 absentees, the Repubicans have a roughly 600-ballot edge, according to the board. But of the 5,906 received to date, 798 more came from Republicans.
These numbers might be good news for Scott Murphy. Accord to the NYS BoE (PDF, p. 9), enrollment in the 20th is 42R-26D-24I. If those percentages had held among the 5,906 absentee ballots returned so far, there would have been 2,468 GOP ballots vs. 1,547 Dem ballots - a margin of 921. But we know that the GOP only has a 798-ballot edge.
Still, as the quoted material makes plain, there's a lot of time for more absentees to come in, and thus plenty of room for these numbers to wiggle. Hang on to your hats.