A pre-production prototype is what you would imagine any prototype to be — the first copies of a design you intend to put into production; that is, it is constructed from the same drawing set that the production units will be built from and largely using the same production methods.
The purpose of a pre-production prototype is to validate the drawing set (master book) through a DVT (Design Verification Test). Typically a lot of development dollars go into making sure the pre-production prototype will be low cost and high quality, and least when compared and contrasted with a MVP or PoC.
A MVP is used to validate the market; that is, to answer some questions, usually an assumption in the pro forma business model, so that the right product is made. A classic example is developing an MVP to measure the demand curve for the product in order to validate the retail price of the product used to calculate the gross margins in the pro forma product P&L.
A MVP can be as simple as a rendering, or a complex as a fully functional product, which may beg the question, why is it any different than a pre-production prototype? The answer is that in an MVP, the design team makes design choices that minimize development cost even if this means increasing the unit cost. This makes sense because the purpose of the MVP is for market validation, not for generating gross margin as is the case for a pre-production prototype.
In an MVP, the design team may take apart another product to use the parts in the MVP, or they may use reference designs. When you are only going to build a few, and it is not clear what will happen after the MVP, it does not make a lot of sense to conduct a lot of DFM (Design for Manufacturability), or a lot of documentation for production.
A PoC prototype is a prototype that is used to determine if the technology is capable of meeting certain technical performance requirements. Generally, a PoC is not even a product — just something to test on the bench.
In any product development project, some requirements represent more technical risk than others. It is often prudent to reduce this risk with a PoC before designing the “low risk” parts of the product.
The purpose of a PoC is to validate that certain performance requirements can in fact be achieved.