The CSC plate is a metal plate riveted to the container door that records approval under the International Convention for Safe Containers, 1972. It certifies two separate things: that the design was type-tested under a classification society, and that this individual unit was surveyed at the plant. Without a valid plate no shipping line will accept the container for carriage.
Before a design can be plated at all, a prototype is tested to ISO 1496-1 under a classification society such as CCS, BV, ABS, LR or GL. The tests are physical: stacking load through the corner posts, transverse and longitudinal racking, floor strength under a concentrated wheel load, lifting from corner castings and from forklift pockets, and a weatherproofness spray test.
Type approval belongs to the design, not to your units. It is the reason a container built this year to a proven design does not have to be individually destruction-tested.
Each unit coming off the line is inspected against that approved design: dimensions and squareness, weld quality, door operation and gasket seal, floor fixing, paint thickness, and the marking and serial number. The surveyor's record is what authorizes the plate for that specific box.
This is the step that a thin supply chain skips. A plate can be bought. A survey record with your serial numbers on it is harder to fake and easier to ask for.
A modern consolidated data plate carries the approval reference and date, the owner or manufacturer identification, the date of manufacture, the container identification number in ISO 6346 format, the maximum gross weight, the allowable stacking weight and the racking test value. Many plates also carry the TIR customs approval and the timber-treatment certification for the floor.
Two numbers are worth checking against your paperwork every time: the maximum gross weight, typically 30,480 kg for modern dry containers of any length, and the container identification number, which should match the unit list on your documentation.
A container is a structural member of the stack once it is loaded. Eight high in cell guides, the bottom unit carries the weight of everything above it through four corner posts. The CSC regime exists because the failure mode is a collapsed stack at sea, and carriers enforce it because their liability depends on it.
For a buyer the practical rule is simple. A seller who cannot show the plate in unit photographs is showing you a problem, whatever else the listing says.