Tuna

A monocoque case has no caseback to read

The titanium case is opened from the front, so there is no screw-off caseback carrying a case number and serial in the usual place. Examiners expecting the standard Seiko caseback layout should not treat its absence as a missing or replaced part. Identification and dating rest on the shroud markings, the movement and the case's own stamping.

6159 parts scarcity drives movement substitution

Servicing a 36,000 vph 6159 requires parts that are no longer produced. Examples exist with movements assembled from several donors. That is repair, not fraud, but it means the movement may not date the watch and should be assessed on its own.