Some things I've noticed, as I'm kinda a hobbyist about this tracking flights stuff.

If the airport tower/ground is broadcast over liveatc, I listen to that.

Unitedcargo does pretty good giving reasonably accurate flight info. Once the a/c pushes, United seems to consider the a/c "in flight". So, the a/c still needs taxi clearance, sequencing, getting the weights, sharpening the pencils, de-icing, wax and wash, position and hold prior to "wheels-up".

Then, good old Flightaware doesn't begin tracking until radar contact is established and I've also noticed a 3-7 minute latency in their returns, compared to my other radar sources, like Passeur.

It's all quite fun to watch/listen to, though

I recall, on a recent MR, listening to a crackerjack ORD ground controller move traffic around the airport as we were arriving was just mesmerizing. Even the pilots were amazed and thanking him (way beyond the norm). Some people just have the gift of doing the job and cracking jokes at the same time

I've gotten so good with the timings that I can actually see my wife's flights arriving (landing) as I pull into our local's cell phone lot. I just don't pay any attention to what UA tells me

Pat