FYI, there was "The" Lambda (Λ) Pro - they were first introduced in 1982. Following are the various Lambda models with the year of introduction (in Japan).
SR-Λ (1979): Normal bias, black body
SR-Λ Pro (1982): Pro bias, black body
SR-Λ Signature (1987): Pro bias, brown body
Lambda Nova Signature (1994): Pro bias, brown body, immediate predecessor of SR-404
Lambda Nova Classic (1994): Pro bias, gray body, immediate predecessor of SR-303
http://www6.head-fi.org/forums/showthread.php?t=150292
Of course, the problem is that Stax occasionally used different naming method for foreign markets, which adds to the whole confusion about "Lambda Pro".
EDIT - That said, I do think these are "the" Lambda Pro/SR-Λ Pro. The only Stax Lambda series model that I'm aware of with black body, thin headband, and pro bias is "the" Lambda Pro/SR-Λ Pro. The auction also talks about SRD-7MK2, which was released in 1985 when "the" Lambda Pro was still in production.