Hello, so we are waiting on my wife's IR1/CR1 visa interview at the US Embassy in Seoul. I have found the NVC stage to be much more opaque than the USCIS stage, with few data points to go off of. So I am posting this information here, in case it may be helpful for others.
So there is a Naver Cafe called Mijunmo ( ) that my wife uses. It is all in Korean though, and obviously focuses on the Seoul Embassy primarily. People there are pretty good on there about posting their timelines, including DQ dates, interview letter (IL) received dates, and actual interview dates. I do speak Korean, so I went through posts there from this summer and last summer to collate those timelines into a spreadsheet. I didn't record every single one cause it was a bit time-intensive hunting through the forums, but tried to get a good sample. I will attach a PDF of that spreadsheet here.
You can see for the past year DQ to IL wait times average about 30 days, and DQ to interview wait times average 80 days. However, do note that recently the Seoul Embassy is taking a lot longer. Many of us who were DQ'ed in May still have not received interview letters (roughly 90 days ago). You can also see in the spreadsheet that there is a lot of inconsistency in how cases are handled. Even though NVC does mostly go "first in/first out" as they say, there are times that doesn't happen. Also occasionally cases seem to get skipped over for later ones.
Seoul Embassy Interview Timelines.pdf