Compressed loads are no different in terms of being safe data as would be any published SAAMI approved data, which they are. The primary reason I load a lot of compressed charges in both High powered rifle and some hand gun loads is because velocities are much more consistent, as are apparent pressures. For instance, IMR-4350 in a .270 win. case at the upper end of the data is a compressed charge. And when I'm loading for any number of handgun cartridges, such as .357, .40, 9mm, I will commonly load compressed charges. Longshot works well for loading safe and consistent stout loads for the .40 and 9mm. For the .357 mag H110 will compress nicely.
In my experience compressed charges don't often produce higher apparent pressures, and often velocities will actually come down slightly too. But as I said, consistency of velocity / pressures have often had a smaller deviation in this respect.
Just don't make the mistake I've seen happen a couple of times over the years by reloaders that failed to read the entire punlished information regarding them. These guys decided to load with a fast burning powder and blew two very expensive rifles to pieces because they didn't know that compressed charges are actually published data relative to slow burning powders. Just imagine what would happen if you stuffed as much as would fit when compressed of a fast burning powder into a .270 Weatherby Magnum case. I don't recall what it was they were using, but it was deffinitely not a powder you could compress and deffinitely didn't have data to support the tremendous load they used. This was a Clark type load, the kind that is used to find the breaking point of any given firearm.
GS