Error that column ID label isn't in either spreadsheet, when it's only missing from one

[MatthewSpofford]

To Reproduce
Steps to reproduce the behavior:

1. Create an original or appending spreadsheet with the desired column ID label
2. Create an appending or original spreadsheet without the column ID label
3. Attempt to merge them
4. Error should be raised

Expected behavior
The error being raised should only occur if both spreadsheets truly don't have the same column ID lab.