A horse would bite off your hand before it'll let you look into its mouth anyhow.
At least my information is coming from the right end of the horse.
And I'm the primary source for accurate ticket information on DisBoards. I maintain the sticky Everything About WDW Tickets in the Theme Park Attractions and Strategies Forum.
And, for the OP, here is my stock answer about Crossover tickets:
Tickets at DL are treated as "straight line" as opposed to WDW tickets which are "front-loaded" for pricing. If you have a valid DL ticket, unused or partially used, you can take it to a Guest Relations Office. They can look it up to see how many days you have used of the ticket. They will then cancel your ticket and apply the unused portion to the purchase of a new MYW (or AP) ticket.
The following is an example with completely made up numbers, as I am not aware of the actual selling price. If you had a five day DL ticket that had cost $200 that is $40 per day. If you had used two days the remaining ticket value would be $120. You would have to purchase, at the very least, a two day base ticket (or a one day adult hopper) to use the $120 and your DL ticket would be canceled.
If you want to use a WDW ticket at DL they will give you a one day for one day exchange, but you can only do one ticket per day per MYW multi-day ticket and the ticket they give you will be good that day only. If your MYW ticket is a hopper you will receive a hopper, otherwise you will receive a ticket valid for one park.
I should have kept reading... Long story short... Reception told me to go to Concierge, Concierge said to go to Guest Relations, and Guest Relations said to go to the Ticket Turnstyle. And keep in mind they mean the Main Turnstyles. I'm staying at the Grand Californian that has its own enterance to DCA, had to hoof it around to the front to enter. Frustrating, depressing, but you still got to play by the rules set forth. Kinda wish I had just bought tickets outright instead of trying to burn off five year old tickets.