The Registration fields (Registration_Current and Registration_Date) are only stored once at a Person level, thus there is no historical tracking of previous registration dates, those values are always going to reflect the current club year.
However, since you mentioned "budget" I think you can instead look at the Fee records to determine the information you're after. On the main Ledger > Fees grid, set the Club Year to last year, then use filters and/or group the records in whatever manner you deem necessary (by Item_Received_Date or Item# or Description etc) and you will be able to get filtered or group Totals to help you analyze the data.
Tip: You can set the "Created" date field to be visible and then sort or group by that column to see when the Fees representing dues (and thus when a clubber registered in mid-year).
