We just moved and got a mattress for free from a friend. I was cleaning the mattress, which didnt have any noticeable evidence of bed bugs, but just smelled bad and musty, but in one crevice I came upon what looked like two cast skins. I put traps under the mattress and today one had a yellowish translucent speck with some brown on it. It was too small too look like anything more than a small rectangle. Couldn’t see any features beyond that. Could it be debris caught in the glue or baby bed bug?
Even baby bed bugs are identifiable to the naked eye, so it doesn’t sound super likely that the mattress was infested. We do have a page that discusses elevating and encasing your bed for prevention and ID which might be useful for you: https://www.bedbugsupply.com/how-to-prevent-bed-bugs.html