A valuation model trained on open transfer markets assumes a club can sign anyone it can afford. Major League Soccer does not work that way, and the difference distorts every number the model produces.
Roster slots are a scarce resource
Squads are divided into categories with limits attached, and each category carries different rules about who may occupy it. A signing consumes a slot as well as money.
Because slots are finite, the true cost of a player includes the player the club can no longer sign. That opportunity cost never appears in a fee.
Models that treat salary as the price therefore undervalue players who fit an unconstrained slot and overvalue those who occupy a scarce one.
Budget charges differ from actual pay
The figure counted against a club's budget is not necessarily what the player receives, because mechanisms exist to reduce the charge in exchange for other assets.
A model reading published salary sees one number while the club is managing a different one. Decisions that look irrational under salary become sensible under budget charge.
Reconstructing the charge from public information is possible in outline and unreliable in detail, which puts a floor under how accurate an external model can be.
Player contracts sit with the league
In much of the world a contract is between a player and a club, so a transfer is a negotiation between two clubs. The league's single-entity structure changes who is negotiating.
That means intra-league movement follows allocation mechanisms rather than a bidding market. Value is expressed in draft position or allocation ranking, not in cash.
Converting those mechanisms into a comparable price requires assumptions that no model can validate, because the equivalent cash transaction never happens.
Outbound sales use a different currency
Selling to a European club is a normal transfer with a fee, so outbound valuations behave conventionally while inbound ones do not. The same player has two pricing regimes.
This asymmetry rewards clubs that develop players cheaply under domestic rules and sell them into an open market. The business model is arbitrage between two systems.
A model that ignores the asymmetry will consistently misprice young domestic talent, because it treats the acquisition cost and the sale market as belonging to one market.
What travels and what does not
Performance modeling transfers cleanly. How a player creates chances or defends space is a football question and the rules do not change the answer.
Price modeling does not transfer, because price is a function of the market's rules rather than of the player. The two halves of a valuation system behave differently.
Analysts working across both worlds keep them separate for that reason, producing a performance estimate first and applying a market translation second.