Also, last time I checked, 35% signed cards triggers a referendum vote, but as GL/OYS says "I may be wrong".
It's only 35% if you don't already have a union. If you already have a union, then it takes 50% +1 to trigger a vote for new representation. Not only that, but the signed cards expire after a year, so many of the DPA's cards are expiring already, and they'll need to collect new ones.