Windows Live Mail Messages Import/Export Query

I have exported email messages from Live Mail previously and have recently done it again, so I now have two sets of backup folders. I have done this so that in the event of having to reinstall Live Mail at a later date I will not have lost my messages. I have assumed that if I had to do a reinstall/repopulate the messages from both backups would effectively 'merge'. On the latest export I note that the messages in each folder (e.g. Inbox, Sent etc) have an accompanying .fol file. However on the earliest set of exported message folders there is no .fol file. Is this going to cause a problem in the event of my having to do a rebuild/repopulate? Thanks