"The good attempts had several flushes before mold set in, "
Many of the commercial kits will grow mold after a few flushes too. Many will only guarantee a first flush. One trick I've heard of is leaving the block in an area with a lot of freash air movement after each flush, even placing them outside.
Commercial shiitake kit got mold on second flush, so I buried it in a raised bed. Nothing happened for a couple weeks, so I stopped checking it regularly, but then found a HUGE (unfortunately old) mushroom (and a few normal sized ones) growing from that spot about a month later. I think burying after first flush might be the best way to go - soil manages moisture and gas exchange needs pretty well already.
Excited to try growing stropharia wine caps soon! PNW is great climate for having a bunch of wood chips on top of garden beds anyways :D
Many of the commercial kits will grow mold after a few flushes too. Many will only guarantee a first flush. One trick I've heard of is leaving the block in an area with a lot of freash air movement after each flush, even placing them outside.