Used the tix last week for myself & DH. Ordered & assigned the numbers to MDE.
we already had leftover non expiry MYW tix, which was the root of our problems during the week. Appears as though the system automatically deducts the tix with the least # of days. It is a known problem that they are trying to fix.
Unfortunately, we also ran into last years'
MNSSHP issue wherein those who enter the party after 4 pm but make FP+, find themselves unable to book one day on their primary ticket media...the system counts the party day against the FP+ entitlement. It's been over a year of working on that resolution with no relief in sight.
became the norm that when we entered a park the non expiry tixs were used vs the
DVC special ones.

First day we waited a half hour outside epcot (I wanted to try to designate the tix being utilized that day before entering the park, but was told to just enter then stand inside at GS again to verify.

).
Another 20 min spent at GS, then routed over to the Magic Band area next door where it took a solid hour to try and fix with multiple CM, phone calls & experts called in to assist.

note that DH & I had to produce driver's licenses, DVC cards & magic bands. The did manage to reinstate the MYW tix and deduct the DVC one day.
the next day we were doing MNSSHP & advised not to wear our bands, only to utilize the tix at 4 pm. that worked well. we were able to book FP+ after 4 pm with the party tix.
our 3rd day we entered MGM. Again, the MYW tix were deducted. I didn't bother to check until the next day inside MK @ GS. Note that two days were deducted from the MYW tix at that point
got it fixed and double checked before we left that
all our MYW tix were still intact and that the DVC tix were utilized. I found it irritating to go thru this on a short visit to the parks. those with a more laid-back personality might view it differently.
I am on the fence as to buying them for my oldest son's family to use since I will not be traveling with them & they also have existing non-expiry MYW tix already linked to their accounts.
we were told that once a MYW tix is linked to your account it is non-assignable or remove-able. too bad, as it would be a simple fix for the issues we experienced imo.