Yes it's changed over time. For most of Westerly history the guitars were shipped with lights, an exception being the period from late '70's-approximately mid 80's when the builds were heavier too. Corona and Tacoma also used lights.
An '06 would be a Tacoma and my memory says they shipped D55's with lights according to their lit.
New Hartford did use mediums, but they also changed top radius to accommodate the higher tension.
Guitars are designed from the start with a certain top tension in mind, and the top is braced to yield best response at design tension.. It's actually possible to "choke" a guitar designed for lights by putting mediums on it, not to mention the absolutely heavier stress on the neck joint.
My opinion, not worth the extra stress on the neck joint for potential volume gain, and likely loss of some of the subtler overtones and sustain due to top being "too tight".