yes, these are above the sea level used by google earth.
if you would use gps coordinates, they would use a different sea level 
basically, the acutal value for the sea level does not really matter as the differences are more relevant than the actual values…
the elev value in the bottom right corner are rounded values, so 1344.501 would become 1345 and 1345.499 would also become 1345 ft.
if you want to know the values up to the centimeter, you can download the kml file I made available to everybody from https : // howdoiknowthisinfo . com / butler / snapshots / snapshot_current . zip
(remove any space between https and zip to reconstruct the url, as the system seems to be unhappy that I am pasting this link…)
when you open that file in google earth, you will find a folder “horizontal planes” in which you can enable/disable horizontal planes at a certain height, e.g., 408.90999999m will show you something like this:
all the areas below 408.909999m above sea level are blackened out…
if you select, e.g., 409.219999m you will get:
this allows you to find the google earth elevation above sea level at centimeter level…
yes, the values I annotated are very accurate and have been established using the method I explained above with the horizontal planes.
the green around building 6 is very uneven as the building is in a depression.
about the way google earth’s values mentioned on the screen in the right bottom: these are rounded up/down to foot or meter level, which is very imprecise…
they use an interpolation mechanism. e.g., if you have a look at the AGR parking, you will see that the elevation is higher between cars that are parked next to one another than around the cars, which does not make sense…
so, this horizontal planes technique is very good to establish the elevation of flat surfaces.
this is what you get for the height of AGR building 6:
so, crooks was looking above the roof that has an elevation of about 413.52m
the pins are where I place the muzzle of each of the snipers:
the top of the roof is about 415.26999m, and I put the muzzle height for the snipers 1 3 4 at 1.2m above the roof top (that is the height of their tripod).
sniper 2 was flatter on the roof, and I put him 40cm above the roof top
the ground level of the south barn is about 409.129999m above sea level:
the ground level of the north barn is 409.44999999m above sea level:
ground floor level for Trump is 409.87m and his ear would be 2.99m above that level, assuming a podium height of 1.2m
I did not model the microphone, but if you subtract about 20cm from Trump’s ear height, that would be reasonable imho…