If the data you want it to "pick" is data from other records that have a year field, then a relationship can be used to match to those records and if the relationship is sorted by year in descending order, the reference will return the data from the related record with the most recent year.
I can't spell out the details for that approach from what little that you have described in your original post.
One record per customer with a field for each year of sales. Now I want to print a customer sales report with only one field for sales per record. Since sales could be coming from one of several fields, I need a method to look for the most recent and report that number in the generic "sales" field.
One record per customer with a field for each year of sales.
That will be a problem. This data would be better off stored in separate related records--which would be required for the method I mentioned in my first post. It would also avoid the need to keep adding more fields as the years pass.