It's amazing what goes on back there on the trailer without any thumps, bumps, or vibration.
I lost a wheel on a loaded car trailer once. I was slowing down for a highway traffic light and the wheel passed me! My first thought was OMG, somebody lost a wheel until I looked at my trailer and realized it was me. The wheel went through a red light, right between 2 cars, did a lane change and passed a car before changing lanes again and running off into the ditch without hitting anything! Amazing and I was very lucky.
I felt absolutely nothing and the trailer felt normal.
I've had 3 very severely shredded trailer tires, again without feeling a thing. One of them totaled my TT with steel belt damage and I didn't notice until I saw smoke in my mirror. And it was a single axle 69 Prowler. Should have felt something with a single axle, but nope! I was towing with a dually. Didn't feel a thing.
So yeah, I can easily see how you never noticed the missing wheel.
TPMS is king! We should all have it.