All personal opinion
Some details....
Depending on your package, or (perhaps)
DVC membership.... You can BOOK ME via MDE or the DVC member site.
Of the two - at least DVC will acknowledge your request.
MDE, however, becomes a black hole, swallowing all data, after you have booked. The reason? The WDW and MEARS computer systems are totally SEPARATE. MEARS (
http://www.mearstransportation.com/) actually RUNS ME - they are a contracted company. And WDW seems to have issues connecting with ANY foreign computer system.... often, their OWN.
Now, the GOOD news....
1) HAVE a WDW Reservation number.
2) KNOW your Airline, and Flight Numbers.
3) When the MDE site throws up, contact MEARS at 1-855-463-2776. You will be talking to ME DIRECTLY. These are wonderful people.... armed with 1) and 2), they will take care of you

. And they are VERY used to WDW Computer System problems

.
Now - SHOULD MDE reflect ME bookings? Yes, it should. The issue SHOULD be trivial - inter-organization DB synch. Wife and I were doing this in 1993. On the other hand, we have not personally associated MDE and basic mid 1990's technology in the same sentence

. That thing is a joke

.
All personal opinion - I'm not right, you aren't wrong.