Sorry if this has been covered, I am not able to access the search function since the new site version.
The Topic:
When did JWs start observing instead of partaking?
I'm embarrassed to admit I don't know this.
I would guess in the early 30's when the little flock/great crowd/we're JW's doctrines were implemented.
Please include references to the publications in your answers!
( did that sound like a desperate plea for comments on the service meeting? I hope so... )