That's what I figured, but a quick check shows only ~7000 unique recipients in transactions.nxt vs. 14,000 accounts in the blockchain explorer:

Code:

$ java -jar jdeserialize-1.2.jar nxt/transactions.nxt | grep -E "recipient: [0-9-]+" | awk '{ print $2 }' | sort | uniq | wc -l
7105

R recipients with negative value included?

Yes, "recipient: [0-9-]+" matches all lines containing "recipient" except for the first one (structure definition).