The reason for your fields not appearing is that Splunk only allows field names to contain a-z, A-Z, 0-9 and _. Any non-allowed characters in field names are converted to . And field names cannot begin with 0-9 or ``. Thus a purely numerical field name would be converted to just underscores, which are not allowed.
You can create fields that have numerical names through a REPORT field transform where you set CLEAN_KEYS = false. (see first link below), but that may not really be what you want, since you might have a hard time to use the fields in certain operations (see second link below).
You might be better off if you could change the CSV headers to start with a letter, e.g. y1960, y1961, y1962 ... y2013.