You certainly should be able to - Since she did not survive him, it is very likely the proceeds would have gone to the contingent beneficiary or HIS estate (she was not married to him so it would go to his family - heirs at law - most likely).
This is not legal advice nor intended to create an attorney-client relationship. The information provided here is informational in nature only. This attorney may not be licensed in the jurisdiction which you have a question about so the answer could be only general in nature.
Q: can I obtain information regarding the plan- to find out if there was a contingent beneficiary listed?
A: I don't think so... your mom has no interest in the plan because she did not survive the boyfriend and there's no family relationship. I'd be surprised if you'd be allowed to serve as the boyfriend's PR and equally surprised if the court would allow discovery if you're serving as your mom's...
Sorry, but there it is...
This is not legal advice. I am not your lawyer. You are not my client. You cannot rely on my response to your question. My response to your question is probably worth exactly what you paid for it. You don't get to sue me for anything. If you'd like to sue me, well you have to hire me first.
Is your mom's estate still open after 9 years? The pension plan proceeds would probably not be an estate asset because her boyfriend survived her. However, if your mom was the only listed beneficiary, the estate may have a claim. You need to get an attorney quickly because there is a good chance that any funds from the pension plan have already been paid out, with the boyfriend dying back in 2012. Don't get your hopes up, but see an attorney all the same just to cover all the bases.
I hope that this answer helps you in a general sense, but it does not constitute legal advice, nor tax advice of any kind, and does not create an attorney-client relationship between you and myself or my firm.