For some reason I've never quite figured, the way many publishers handle anthology payments is that they pay the editor the entire funds budgeted for the book, and the editor pays the creators for each story. This is not always the case, but often.
Subsequently, because the publisher has treated the editor as a kind of sub-contractor on the project, any royalties earned are forwarded to the editor who is then obliged to send a pro-rata share to each author, depending on the percentage of the book contributed by each author. For instance, if it is established by contract that an author will receive 10% of the royalties earned because his story encompassed 10% of the anthology, then if the editor is given $2,000 to disburse among the contributors, that author would receive $200 in royalty payments.
Some years back I sold a story to the anthology CHILDREN OF CTHULHU published by Del Rey Books and edited by John Pelan and Ben Adams. For whatever reason, of the two editors, Pelan was given control of the purse strings on the book. I was initially paid for my story, but have to this date never received a penny earned in royalties. This despite the fact that the book is still in print after a full decade and seems to be a perennially good seller for Del Rey Books. I've inquired to find out why I've never received any royalties, but no good answer has been forthcoming.
Of the two editors of the book, the only one I speak to is my pal Ben Adams who has always stayed in touch with me. He, too, has never seen a penny out of the anthology's royalties, despite being the co-editor. I've been told that all such funds are forwarded elsewhere. Del Rey has never bothered to clear this up with me, so I have no idea where. Neither does Ben. I've never been able to get in touch with John Pelan about it.
I have only co-edited a single anthology in my days as a writer/editor. That was EVERMORE for Arkham House Books. Before her death, I was told by April Derleth (the publisher) that she thought she owed us some royalties, but she never made that clear. Since her death I've not heard from the folk who are in charge there now. I was happy when Arkham House actually cut each check for the authors in that volume, so I assume they'll do the same when (and if) the book earns out royalties.
Other anthologies of which I have been a part have paid out royalties regularly and with perfect accounting. Especially when I sold to anthologies handled by the late Marty Greenberg.
Will I ever be made aware of, or receive royalties from CHILDREN OF CTHULHU? Who knows?