HR question...

After being a stay-at-home-mom for a year, I finally re-entered the workforce after searching for four months for a job. I've been promoted on every job I've ever held, even making it to Supervisor at the last one prior to having my daughter, and four months is the longest I have ever searched. In each of the interviews, it seemed as if the employer was excited about my qualifications, with one company all but stating that I'd be called back for a final interview...then, nothing.

Now I know this can be due to many reasons, but I can't help but wonder if a poor reference from my last employer had anything to do with it. I was an inventory supervisor, and had the hardest time staying on top of missing items, although in the end I always found everything, even if it meant putting in tons of ridiculous overtime. I always felt like I was not getting the support I needed from my boss, even though he always verbally assured me he was on my side. Since leaving that company, I heard that my former boss has been fired for stealing, which would explain the inventory issues I was continually having. Also, something about his mannerisms never made me feel like he was really on the up and up, and even though he always said he thought the world of me and my abilities, I wouldn't be surprised if he gave me an absolutely horrible reference.

I tell this story to ask this: how would I ever be able to find out if he had given me a poor reference? I know for a fact in my state that it is illegal to give any information other than confirming whether or not someone had indeed been employed, and I have heard it is the same in many other states as well. But, how would I ever know if my previous employer broke the law if his reference caused someone else not to offer me a position? It's not as if the company would tell me that my reference was bad, they would just say they'd decided to go with someone more qualified. Also, if I was able to prove that the law had been broken, would I be able to sue, and on what grounds? And just so things are clear, I only listed my former boss as a professional reference, not personal, simply because he was my supervisor at my last job.

Can any of you with some HR experience dispel my curiosity?