I agree that there is conflicting information about Lavender pruning.
I think some of the reasons for different pruning recommendations is that you do prune differently with 1 year old plants vs more established plantings.
The first year you should pinch out the flower heads only.
After the first year prune in early spring, just before new growth starts. Cut back 1/3 of the plant and shape into a tidy mound.
Do not over prune or go into the woody stems.
Older plants (3years of age or older) should be pruned only lightly and only on the new soft growth. Do not cut into the woody stem.
Prune older plants in the summer as this will promote new growth.
When in doubt prune less!