I've linked my park tickets (10 park nonexpiring tix) to my MB for a trip in June. I haven't received my MBs, yet. If I go to WDW before June, how do I use my tix, if I don't have the MBs by then?
You won't receive your bands until about a month from your trip. And even if they did really get lost in the (UPS) mail, the hotel would just issue you a new set at check-in. Nothing to be concerned about.
The tickets are what they are. They are added to your MDE profile. The band just accesses that. Any duplicate band would be able to access the tickets, as long as they are linked to your MDE.