In some cases, backups from older versions of Android can lead to the creation of complicated vCard files that have old formats. If someone attempts to convert vCard Contacts into a CSV file, they might see that certain fields, like birthdays or notes, are gone. The main point is to make sure that the VCF file is not only partly corrupted. Look at it in Notepad first and see if every contact is followed by BEGIN: VCARD. You need tools that can open older versions to be able to read them. WholeClear vCard to CSV Converter is a good tool that can handle files that are generated from older mobiles in a very reliable way. Besides that, there is also a possibility to export contacts once more from the phone by means of the "Share as VCF" option; those files usually are of a higher quality. After the cleaning, the CSV file will be regular.