I have only known my wife since early march 2011. In the end I printed off a full days worth of YM chat for one sample day a week, since we met.
In YM I pressed the save button which created a text file then printed the text file.
My only misgiving is the chat isnt dated like it is in Skype. I hope it will be ok for that. I wrote the dates at the head of each days worth on the first page. (Sometimes the dates are reasonably obvious to the reader as they tied in with visits and plans of ours).
I did also include prints from a small selection of email exchanges and some printed Skype material in our box of papework for VFS.
But we mainly used Yahoo Messenger as our medium of communication.
Also sent 46 photos of us both together for two visits to the Philippines in June and April 2011
It remains to be seen if it is adequate or not.....