Like Geoff said, three different species have been used somewhere in the ancestry of your orchid. 'B' for Brassavola, 'L' for laelia and 'C' for Cattleya. Many of the laelias have been reclassified as cattleyas so the 'L' may not be needed. I'm not sure what has happened with the classification of brassavola. Like Geoff said, many orchid growers still use all three letters.