Can someone ask about past business events on Shabbos?
An example would be: I bought an investment property two years ago for a crazy good price because the seller just wanted to offload the property asap.
Assuming everything has been completed from that deal, it is permitted.
Shulchan Aruch Orach Chaim 307:6 writes this explicitly; see Mishnah Berurah and Aruch Hashulchan for further details, including the suggestion that one nevertheless refrain from such idle talk, even though it certainly does not violate the prohibition of discussing business:
אסור לחשב חשבונות אפילו אם עברו כגון כך וכך הוצאתי על דבר פלוני ודוקא שעדיין שכר הפועלים אצלו אבל אם פרעם כבר מותר:
It is prohibited to [discuss] calculations, even if they have passed, e.g., "I spent such and such on such a thing", but this is only if he has not yet paid the workers, but if he already paid them, it is permitted.