I hate to be a killjoy, but it’ll clearly be a single deposit layer dated to on or after the latest date-able item. The fill will all be the same and its own distinct layer against the rest of the area. If you have a long enough time to keep it open, want to dig more, and have different fills, you might be able to accomplish something, but the different fill materials would likely have no real match in the surrounding still making it obvious.
Expected treasure, but safe contained a live panther; would not buy again.
apologies to XKCD