severe sentinel
Some time in the last seven years the event currencies got changed from a inventory item into a currency (good change). I still have some of the older items. The Gree ones specifically mention they can be exchanged at the Gree Reputation Vendor on Ilum but I don't see anything that will do that.
clear pewter
try mailing them to one of your other characters and when you accept them from the mail, watch if they get added to the currency page instead of the regular inventory.
severe sentinel
Tried both that and passing via legacy storage, no joy. From what I've read both of those worked before 7.0 and apparently the currency tab was not shared across the legacy.. The only other thing I've come across is to file an IG bug report.