I can't figure out how the RAM limit works (asus sabertooth x58, i7 990x, 2x 8GB & 3x 4GB)?

Question

Iron

Good afternoon, I decided to insert an RAM more than the maximum declared volume and surprisingly it worked. Although the manufacturer's website indicates that the maximum amount of memory is 24GB, and I have 28GB. In addition to all this, it’s not entirely clear to me what the frequency is, on the site the maximum is 1066, they work for me at 1600. Can you explain how the volume limit works and what the deviation from 1066 affects?
Sticks: 2x DIMM2: Kingston HyperX KHX1866C10D3/8G, 3x DIMM5: Samsung M378B5273DH0-CH9.