The "compromises" aren't necessarily in the form of legislation.
For example, during the 1992 election, an incumbent Democrat, pro-Brady, pro-Assault-Weapon-Ban, was running for reelection against a challenger, Roscoe Bartlett. Despite his positions, the NRA gave the Democrat an 'A' rating and endorsed him over Bartlett, who was anti-Brady and anti-Ban. The sole reason was that the incumbent Democrat was projected to win, and the NRA wanted to curry favor with him.
However, you mention the Brady Bill. NRA came out SUPPORTING it as long as it had their instant-check provision. Many members, myself included, screamed and ranted at the NRA leadership, telling them that an "instant check" was a superhighway to a permanent computerized database. Did the NRA listen? Oh no, they had to have their instant-check grafted into the bill.
You call it the "national gun registry (for a whopping 24 hours until purged)" -- you seem to be studiously ignoring the fact that the feds weren't purging records after 24 hours, they were keeping records for months until Ashcroft got in (and even now, who knows if they're really purging the records). And you seem to be unaware that they were making, and kept, backups of the database, at least during the Clinton years. PERHAPS that has changed, but there's no problem in making daily backups just before the day's data gets wiped; one of my former employers (which had a mail-order catalog) did exactly that with their daily transactions.