Great article!
From a fishermen's perspective, it's fine to leave rotunda and invaria separate because it highlights the range within this species. But as a technical correction, entomologists have now determined that they are in fact the same species. The sulphers are down to 2, and rotunda was left out of the mix. Invaria range in color from olive to brown to yellow, in sizes ranging from 12-16, and inhabit generally medium current areas. The spinners are generally "rusty" colored, but more grayish red than say, March Browns. The dorothea's are indeed smaller, inhabit slower water, start a week or two later (but overlap), and a pale yellow or white as duns and also paler as spinners, sometimes with a yellowish orange tinge.
It is somewhat important to distinguish between the above "sulphers" and the other yellow mayflies. Hatching behavior is very different. The above sulphers do swim to the surface as nymphs, and emerge from their shucks on the surface. This makes emerger patterns extra important, and brings floating nymphs, trailing shuck patterns, and the like into the equation. The cahills of the maccaffertium genus, on the other hand, are clinger nymphs and thus emerge primarily in or near heavy riffs. They crawl along the bottom to slow, shallow water (usually edges) before emergence. So you fish them in different areas, with different tactics. Epeorus vitreus (pink lady) is yet another clinger, which emerges on the bottom and "flies" to the surface as a dun. This makes floating nymphs unimportant, but swung soft hackles very effective.
True sulphers have 3 tails, not 2. If the hatching bug doesn't have 3, focus more on riffs, because it's a cahill or a pink lady, not a sulpher.