The search for early references requires a fair bit of time and effort. I've struck up relationships with a number of established collectors as well as merchants who possess - or have possessed - some of his work in recent times. Let's see if that pays dividends.
There has been a dramatic uptrend in asking prices for early-to-mid period references in the last three years, not to mention wide variations in valuation. One merchant, for instance, currently has on offer pieces with asking prices between 50% and 300% above for exact same pieces with identical accoutrements. This on top of a sketchy grasp of the watches' specifications. This isn't unusual: the shared knowledge base is quite modest.
Having consulted Europa Star from 1989 to about 2005, it does seem that most if not all DR watches in mint-to-very good condition are available today for well below their original MSRP (notwithstanding the example above). This suggests that they remain undervalued, and implies the market has yet to fully recognise and price in their significance. This is a working assumption I'm willing to work with given how much influence Daniel Roth had: on Breguet, Lemania (and by extension Patek Philippe through their use of his iterations), his eponymous brand, and Bvlgari.
I regard him as a standard bearer of Anglo-French classicism, one of a quartet whose work is and will remain timeless.