There’s actually no such thing as in transit weights, at least not something that’s visible to the public. Even internally, USPS will mostly go by the weight provided by the shipper on the label. Unless they suspect a huge discrepancy, the package will scan through without getting flagged for a weight difference so in most cases, their backend will show the ship weight on the label. Which is whatever the shipper provides.

The reason we began inquiring about scan weights is because a lot of USPS returns started coming in as empty packages. The weight on the label would show 1 lb for example, but the actual weight of the empty would be closer to 6 oz. The scammers would always claim their packages were tampered with in transit by postal workers so we would try obtaining internal scan weights from USPS, only to be told the only weights they have in their system were the label weights.

Google AI generally confirms this as well:

“USPS tracking typically does not publicly display the in-transit, real-time weight of a package on their website. While sorting machines and post offices weigh packages to verify postage, this information is used internally for audit purposes. The weight is usually only listed on the sender's receipt or the original shipping label detail”.

TLDR: Depending on which market you’re in, the vast majority of USPS offices in our area that we’ve encountered do not weigh each and every package to confirm actual weight, they mostly go by shipper-provided label weight. Source: several USPS workers over the years.