i have experienced this.. if there are a ton of assets that are fully depreciated I have added up those particular assets and created one asset for the totals.. items that are not fully depreciated i entered individually..

now one shortcoming of this method if the company sells one of the assets fully depreciated you will not be able to mark that one "composite" asset as being sold.. you could at that point though carve out that one asset and create an asset for the item being sold.. but you would not know the cost unless client knew or you can keep the "old" depreciation schedule to find the cost there. 

i know this is not the best method but it can be a workaround and as far as these old assets, i have not seen clients selling old assets.. it could very well be that some of those old assets don't even exist anymore and were never taken off of the fixed asset listing.