It turns out I had a 96% survival rate. Out of 102 cocoons only 4 didn't make it. And those are inside and could potentially still hatch.
96% seems like an excellent survival rate. That includes the cocoons being teased from the trays, washed in a weak bleach solution and fresh water. Then stored in an airtight cooler since November out in my garage. I think this incredible survival rate can be attributed to the cleanliness of the houses, free of anything that might kill a young mason bee. Some bees have been active now for about three weeks. I already have 12 holes completely filled with eggs and mud in my tray houses. Next October I hope to gather nearly 500 cocoons.
98 survivors vs. 4 non-survivors.
Two bees mating in the release box surrounded by discarded cocoons. The releases boxes were also fun to look into periodically and watch bees chewing through their cocoons.