Mine has had 2x4 in it since app. 2010. I tested it in the shop so I knew it worked and right after I walked out of there I called one of my nerdy friends and we talked for a very long time about the an obscene amount of RAM I had.

That machine developed a screen fault later, but I replaced it with another X200, which is still my personal machine. I have a T490 for work and the experience makes me want to stockpile the older models.