A composite watch combines period-correct components of different origin: a movement in a later case, a redialled face carrying a more desirable name, replacement hands, or a case back from another example.
This happens for ordinary reasons — repair, salvage, fashion — long before any intent to deceive. That is precisely why composites are common and why detecting them is research rather than accusation.
The method is internal consistency. Does the case size suit the movement? Do case hallmarks and movement date agree? Does the dial's feet position match the movement's dial plate? Does the signature match how that firm actually marked its work?
Redialling is the most frequent alteration. Repainted dials often show modern lettering, wrong fonts, filled-in seconds tracks or signatures applied over old enamel damage; a dial maker's original marking is easier to verify than to fake well.
Conclusions should be proportionate to evidence. 'Movement and case are both period but the pairing is unverified' is honest; declaring authenticity from photographs alone is not.