GC approved - Who is financial sponsor?

My marriage based GC got approved a few weeks ago but I'm not sure who is liable for me financially.

When I first sent out my AOS package, I only had my wife, who is also my I-130 sponsor, fill out a I-864 as the primary sponsor.

Unfortunately after completing my Biometrics I received a RFE from USCIS because it turned out that my wife's income wasn't enough for the last tax year (It was like $50 below poverty minimum).

Luckiliy for us, I got the RFE during the new tax season, so my wife and I filed again and this time her income was above the 125% poverty minimum. Not much, but she was above.

Since the RFE more or less recommended including a joint sponsor, we went out to look for one even though in theory new tax year should have shown USCIS that she now made enough.

We replied to USCIS by including a new I-864 from my wife with her new tax year income and also a I-864 from a family friend who volunteered as a joint sponsor . The friend's new tax year's income was around $5k more than my wife's.

A year later I had my interview together with my wife. During those 20 minutes we spent talking to the Immigration Officer, the topic of the RFE was only brought up once.

It was IO: ".....and you send us your reply to the RFE you received a while back, correct?"

Me : "That's correct."

Another 9 months go by and finally my GC got approved but now I'm unsure whether it's just my wife being financially responsible for me or if USCIS also used the joint sponsor as a back up.

Like mentioned at the beginning, my wife's new tax return that we filed during those 90 days USCIS gave me to reply to the RFE showed an income above the 125% poverty minimum.

Is there anyway I can find out? I would like to let the joint sponsor know if they are indeed currently responsible for me or not.

Thanks so much.