Excel does some odd things when you try to copy table data from one workbook to another using a simple copy-and-paste. I can't quite figure out what it's doing.
But I do know of two ways to get things to work the way you want them to work. If you don't mind importing the YouTube networks again, here is the simple way:
1. Import the first YouTube network.
2. Uncheck this checkbox in the Excel ribbon: NodeXL, Data, Import, Clear NodeXL Workbook First.
3. Import the second YouTube network.
Because you chose not to clear the NodeXL workbook before importing the second network, the second network will get added to the first network instead of replacing it.
If you can't import the YouTube networks again, here is one way to copy-and-paste data from one workbook to another. It requires a few more steps than usual.
1. Select and copy the data from the first workbook.
2. Click the cell in the second workbook where you want to paste the data. DO NOT PASTE THE DATA.
3. In the Excel ribbon, select Home, Clipboard, Paste, Paste Special.
4. In the Paste Special dialog box, click Values and click OK.
5. In the Excel ribbon, select Home, Clipboard, Paste, Paste Special.
6. In the Paste Special dialog box, click Formats and click OK.