If you cross-threaded the fitting into the MC, and kept going, that's bad... I've never had much trouble getting them back in but occasionally you'll get one that's hard to start because the line got bent a bit - it's got to line up straight, then the fitting should spin in by hand. If the fitting is mangled but the threads in the MC still appear OK, then the flare can be cut off, a new fitting slipped on, and the line reflared - there's enough line to do it. If the MC threads are messed up, I'd try to run a new fitting (not installed on the line) STRAIGHT into the MC, using a socket & ratchet to keep it straight. If the threads start to pull out, it's time to try again with another MC. FWIW I've had a couple reman calipers with bad threads, appeared to have been cross-threaded then re-tapped, crooked, so the flare wouldn't seat & they leaked. Perhaps that's what you're up against here.
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Chris, Dartmouth NS Canada 70 M-B 280SE, 83 245DL, 84 244 turbo, 90 780 turbo, 92 VW Golf, 90 740 Rex/Regina