Indeed, for a quick look into a .csv file with SAS, the IMPORT procedure is convenient. It can also generate a code template for an import data step. But when used for production purposes, those convenient automatisms constitute a risk. From a QC point of view, a procedure statement called "GUESSINGROWS" should make the alarm bells ring.
Still, I am curious about the reason of those length discrepancies. If I were to track that down, I would reduce/increase the actual length of the affected string, in order to find out exactly where the discrepancies start. Then I would make other small modifications to the file, and so on.