No, it's "When life gives you lemons, you make lemonade, but when life gives you oranges, you make grape juice, just sit back and let the people wonder how you did it." What you want are called rom managers. However, these can potentially be confusing to use, so I won't be recommending those to you just yet. What they do is basically compare your romsets to a DAT file that contains information about known romsets (size, name, length, CRC, etc.) and based on the comparison, can tell you if your romset is corrupt, missing files, wrong sized files, etc. etc. DAT files exist for almost every emulated system and its roms. Does Nebula say what files are missing and what it is expecting?