More information on IR protocols, limitations of the IRremote, and solutions for those limitations (MSB vs. LSB, long IR signals, unsuported protocols etc.), vsit documentation or webarchive entry.

For MSB/LSB debug use the reverseBitsSignificance function available in code, or online tools such as HEX to BIN, bits reversal, and BIN to HEX.

As for the NEC protocol, if you encounter a 0 signal (LSB, FFFFFFFF in MSB), thats a 'repeat' action, whitch means 'the same key as before, continuously pressed'.