I think the problem here is that
L cachinnans when originally split from regular Herring gull did include
L michahellis, and the combined species was called yellow-legged gull. Then in the following split,
michahellis inherited the "yellow-legged" name and
cachinnans became Caspian Gull. Now with regards to Opus, all our authorities accept the first split while only Clements accept the second split. So formally, the situation in the taxonomy template is the correct one.
In Opus however, we do have entries for both
michahellis and
cachinnans. IF we follow our own rules, we probably should merge these; however, I am afraid that some birdforum member would be unable to understand that situation and make a new entry for the one that would be missing. Another possibility is to say that this is a split that is so well founded in strong data that it should be in Opus already now, but I don't know the data well enough to be able to say that, and I don't know if anyone else do; there are some threads in the taxonomy section about gulls to peruse. Third possibility is to break another of our rules and have a page for the second of these which we label as a subspecies page (writing something like
Larus c. cachinnans).
So in the end, I am not sure this post solves any problems
Niels