Why are there multiple accession numbers for a cDNA clone?

In short, all the accession numbers are relevant to the clone. Some records are the result of quick sequencing end reads and others from a full sequence read of the clone/insert. Full sequence read accessions always start with "BC". *Additional details IMAGE clones are generally sequenced on one end first (for newer clones it is the 5' end). This is because IMAGE makes MILLIONS of clones looking for full-length ones and it is too expensive to fully sequence all clones. So, they use the initial 5' end read as a screening tool to look for start codons and to see which clones are worth their time and money to fully sequence. Once they get that 5' end read, it gets a GenBank accession and the sequence is posted on GenBank. If they fully sequence a clone, that sequence also gets posted on GenBank and gets a different accession number. Full sequence reads always start with "BC". So, for clones that are fully sequenced, they should have a minimum of two sequence reads posted on GenBank. One is the initial 5' end read (which can start with anything except "NM", "XM", or "BC"). The other is the full sequence read of the clone - the one starting with "BC".