Are the dates (e.g. 22-Jan) date formatted? My guess is they are and are actually 20th or 21st century dates (thus the need for the year field since Excel can't handle dates prior to 1/1/1900 as it does dates thereafter).

If that's the case, then Field 2 can be populated with the Day function and Field 3 can be populated with the Month function. Obviously, Field 4 can be directly populated. Field 1 is then just a concatenation of these.

At any rate, if you post a sample of your sheet, it would make it easier to see how it needs to be done.