This is all so typical. He knows you're entitled to half of his retirement plus alimony, but if he can guilt you and make you feel badly for him, hey why waste the shot? This is where being your own best advocate comes in. You have a lot of years left to live and you will need that money. Money that is rightfully 50% yours!
I would imagine the difference in having your signature the first time around was because you were on the registration and you were cashing in stock. A retirement plan is a whole different thing. Even though you are the bene only his name is on the registration. Some company's are very lax with the spouses signature, but that is the law! Also as I said before he could have forged it. My ex freaked when I called him on it. Heck, I guess he forgot that I would know this stuff considering what I do for a living. I think he may have wondered just a bit if I was going to turn him in.
My best advice is to take everything that is rightfully yours. If you think that there may be another retirement account that you may not know about, have your lawyer suppeona his former company. No company wants to get tangled up in domestic issues, so they are very prompt in getting out the information requested.