Future Years Depreciation and Last Transaction Dates

I work in a utility company where we have many long life assets - hundreds of thousands of assets which have life 60  years. In order to limit the size of our depreciation tables we have limited our "Future Depr Yrs" in book to 10 years or so. However each year we need to create the depreciation open transactions for all assets or we would only have 9, 8, 7 etc future years depr as time goes on which doesn't help our planning... However running the open transactions for future years depreciation requires the entry of a Trans Date, usually