Short answer: yes, most of our knowledge is not from seismics and geomagnetism, but from experiment and measurements, deductions from geochemistry and -physics, material science and physics in general (besides the already mentioned measurements of earth's gravity, but the variations are rather connected to mantle convection, water storage, etc. than the core)...
There are three ways samples of the mantle could arrive on the surface of the Moon.
Drilling deep holes into the mantle, take a sample and send to the
As ejecta from a large deep impact crater, particularly where the
crust is thin.
During volcanic eruptions, the upward moving magma tears of chunks
of mantle from the walls of the volcanic "vent" and ...
I found the picture with a small write up on a JPL site.
It's a picture of the Aine Corona with pancake domes.
This Magellan radar image shows a region approximately 300 kilometers (180 miles) across, centered on 59 degrees south latitude, 164 degrees east longitude and located in a vast plain to the south of Aphrodite ...