I've appraised several by such architects as Richard Neutra (also a student of FLR), Stanford White, Norman Jaffe, Polhemus & Coffin, etc.
I really don't see value in the fact that a particular person designed the home, with the possible exception of extremely famous architects. Stanford White and Frank Lloyd Wright are some examples. However, even in the case of Stanford White, the particular type of homes he designed are of very high quality, are timeless, and appeal to the wealthy clientele. Other homes of similar design and quality seem to bring similar prices.
There could be particular exceptions on specific homes. For example, Norman Jaffe designed many contemporary-style homes that have a FLR influence. Many of his homes have been bulldozed due to the dramatic increase in land over the past several decades. However, there have been some notable exceptions. On Jaffe home had a particular type of California Redwood with very dramatic coloration, and this particular home sold for a ton of money. If it didn't, it probably would have been bulldozed.
The long and short of my ramblings is that it is difficult to determine an adjustment for a particular architect. It's probably limited to extremely well known examples of the architect's work, and would probably have some type of historic/landmark status anyway.