Adding additonal data to a print merge. Corel Draw won't include it.

I'm doing a print merge from a .txt file with 2 fields.  I can print the original data just fine, but later,  If I want to add more data, how do I get Corel Draw to include it in the merge.  For example, the first field is numbers 1 through 10.  The second field is letters a through J.  I print that.   Later I want to run another print but I've now added numbers 11-26 and letters K-Z.   When I run the print, Corel Draw still only prints the original data.  So far, the only way to get it to include the new data is to edit the merge fields in Corel, delete them, re-add them and it works.  That can't be the correct way.  There should be an update or live link.