That’s actually very easy to do.
Let’s use a package coming from ABQ to Chino, CA (near ONT). The tracking information from UPS says the package processed at their ABQ facility 8:42 p.m. MDT today. I look up flights from ABQ to ONT today. I notice that UPS has a flight from ABQ to ONT that departed on 9:00 p.m. MDT There’s a great chance that the package was on that flight (UPS887).
You can also confirm that after the flight has arrived. UPS887 arrived at ONT at 9:21 p.m. PDT. You see that the tracking information shows the package was processed at 9:44 p.m. PDT I’d give great odds that UPS887 was the flight the package was on.
Same process works even if the package is indirectly routed to your location. Just check the times and compare it to the UPS (or whatever carrier). It’s just as easy to see if a package went ABQ-SDF-ONT as it is nonstop.