If you navigate to add.php?reference=1 the session should be:
,1
Then if you navigate to add.php?reference=2 the session should be:
,1,2
/portfolio.php should then produce:
1
2
Which is the point where you'd want to look up the reference in the db and get more details. If you're doing all that, and getting something different - let me know and i'll run it here. | 
