Thanks to June for posting this information.
I would like to add one thought for people whose interest in data from Robbins & Easterla is for the purpose of checking on an early or late record or other non-seasonal occurrence.
If you are wondering whether your observation of a certain species is early enough, late enough, or far enough out of season in any respect to merit documentation, I would be glad to help. Please email me at the address below and I will let you know my opinion.
I should add that the MBRC does have definite guidelines for documentation in terms of rarity; if a species is listed as "accidental" or "casual", it needs to be documented, and if merely "rare," then it does not. This usually clear from the Annotated Checklist and the Review List, both on the ASM web site. We don't have such clear guidelines for early/late records, so to some extent it's a judgment call.
Hope this is helpful, at least occasionally.