I know you're looking for responses that were done prior to Covid, but I'd like to offer my 2 cents...
I submitted an index request in December 2020 and then another request in February 2021 once I found my grandfather's file number on my own (through his Petition for Naturalization). I've sent various emails to the genealogy email (genealogy.uscis@...) and have received responses to my questions. I most recently sent a FOIA request and when I checked the status online, I've moved up in the queue and my expected response date is 4/23/21. So, it seems like everything is up in the air.
I recently sent a status update request to the genealogy email (genealogy.uscis@...) and this was the response I received:
"We process our requests on a first in-first out basis. Index searches take an average of 120 business days to complete and you will receive your results via e-mail.
A records request requires more time and normally takes an average of 140 business days to complete. If your file not digital, and located at another facility, it may take longer as several of our facilities are still partially closed due to COVID-19. You will receive the record results in the mail.
We had an influx of requests between August and December 2020 that caused a 40% increase. Please understand the times are an estimate only and can change often based on various staffing issues and file locations.
We are processing requests received on September 25, 2020.
We are working diligently to reduce our backlog, but we are short staffed as well.
Your continued patience is appreciated.