Data Range Insanity

I have an Excel template which I use every month; and every month there is a different amount of data that goes into it. A couple months ago we had a mega-data month, with 47,000 records; however, most months, like this one, have a record count merely in the hundreds.

Problem is, when I go into the Excel template, do a CTRL-END to get to the end of the 47,000-record dataset, then delete all of that data, Excel keeps thinking that's the end of the file. Then, when I paste my new data (in this case 450 records) into the spreadsheet, and try to go to the end of it with another CTRL-END, I end up at the end of that 47,000th record, instead of the end of my new data block.

I have tried everything from CLEAR ALL to deleting all of the superfluous rows, but nothing seems to do the trick.

Am I being dense?