I no longer live with my parents (who are not frum), but I do keep items there for when I come to visit.
I am generally careful not to sell chametz gamur over Pesach (aside from some very expensive liquor). Before Pesach, I cleaned and checked all areas I believed contained items that belonged to me, and brought all potentially chametz items to one location in the basement, which I sold through my neighborhood rav.
Upon returning home several weeks after Pesach, my mother informed me that she had moved some of my foodstuffs BEFORE Pesach, and had neglected to tell me. These items included unopened boxes of pasta.
My question: even though I generally wouldn’t sell pasta, and despite my knowledge of its existence, plus both my mechira and my bittul, am I now allowed to eat this pasta?
Although you didn’t know about it, the pasta was automatically included in your sale, provided you signed on a standard document of sale, which included any chametz you have anywhere in the house. Assuming that this was the case, it is permitted to eat the pasta.
For general principles of mechiras chametz, see our article on the topic. Although some prefer not to eat chametz that was sold, the basic halachah and the general custom is to be lenient, and provided the pasta was included in the sale (as above), there is no difference between the pasta and the liquor.