Hi Neesie,
I will tag any blocks that the maker lets me know that they are unwashed for sure! In the past I have never had one person let me know one way or the other about any unwashed blocks.
I do understand the concern completely. If you are going to spend that much time money and effort on something, you want to be able to wash it with confidence that something isn't going to run or shrink up.
Please anyone who could not wash their fabrics let us know, ok? We want to avoid heartbreak.