I've said it before and I'll say it again now. There's a reason oyster shelfs are on the cover of the Missouri Mushroom Guide. Glad you found them.
Back in the '80's when I worked for Union Electric, we were electrofishing on the Missouri River about this time of year. Got out to take a break a mile or so above Labadie. It had flooded a couple of years previous, The place we got out was covered with dead willows and sycamore, down everywhere. They weren't big, most about four to six inch trunks, They were covered with oyster shelf. Three of us filled trash bags with them. Ate. froze, gave away and just had way too many to deal with. Never have seen the like since. But they are good fall/early winter producers. You do have to find them fast, the deer and every other living thing in the woods will eat them as soon as they find them.