Maybe this will help - or maybe it will add to the confusion.
From Bodjidar Dimitrov's excellent website:
"During its long production rung, the Pentax LX was updated at least three times. The latest camera revision has three visible differences compared to the earliest: there are two white points missing on the front of the first shutter curtain; pressing the button that releases the viewfinder causes the light meter to turn on, and the shutter-lock switch features a new design.
Severals attempts to gather information about camera serial numbers and design variations have failed due to inconclusive data."
LX*(late*version)