Consequence of shifting carry-on luggage to checked luggage for aircraft weight

Does the average weight calculation for passengers on commercial
flights include an allowance for their carry-on luggage?

The reason I ask is that, if the carry-on weight is shifted to the
hold, calculations that use an assumed average weight for passengers
and their carry-ons in conjunction with actual weighing for luggage in
the hold may produce estimates of take-off weight that are too high.

For example, if the average passenger has 10 lbs of carry-on and this
is incorporated into the estimated weight used for that passenger, and
he is suddenly required to check the carry-on, the assumed weight will
be too high by 10 lbs. This, combined with the 10 lbs extra of
measured weight in the luggage in the hold, would make the take-off
weight calculation 10 lbs high. Multiply that by hundreds of
passengers, and you have a weight that could be thousands of pounds
off.

Has anyone considered this? A too-high estimate could affect flight
characteristics and might also waste fuel (since more would be loaded
than needed).

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