It appears from presentations I have attended that cDNA often lacks terminal sequences (usually 5′) which have not been copied from the mRNA. This puzzles me a lot, but I have not been able to find the answer as the focus of most of the sources I have consulted seems to be the principle, rather than practicalities.
Does reverse transcriptase just fail to finish copying the mRNA sequence, and if so, why? Or what is there some other problem? ?