If you take a look at the AOS process spreadsheet, you will see where it clearly says some FOs are still denying cases filled prior to the month in which they're current regardless of what the memo or even the USCIS website says about early filing. (The memo by the way was intended to be a recommendation for the FOs, it does not confer a right on petitioners who opt to file early). The process, in the past, used to be that your AOS package cannot be received before the first day of the month in which your CN is request. For instance if you're current in Oct, in order for your petition to be considered properly file it cannot be received at the Chicago Lockbox before Oct. 1st. So if your CN is current in Oct and you filed in Sept, that
IS early filing.
So my suggestion to you when you do visit your FO is not to focus or refer to the IO in charge of your case as being 'picky'. Politely request to know the reason for the denial. If they confirm confirm it's due to early filing, calmly explain the fact that you filed based on what's written on their website as follows:
"Section C contains a chart showing the Diversity Immigrant category rank cut-offs for the following month, which represents the advance notification of Diversity Immigrant visa availability. As soon as a monthly Visa Bulletin is published, anyone with a lower rank number than the rank cut-off number shown in Section C is eligible to file for adjustment of status. This provides lottery winners the opportunity to file for adjustment of status up to six or seven weeks before a visa number can actually be allocated. This gives USCIS additional time to determine your eligibility for adjustment of status before the end of the fiscal year."
Do print out the page by the way:
https://www.uscis.gov/green-card/ot...card-through-diversity-immigrant-visa-program
Use the memo as additional/back up evidence. If you rely on the memo alone or use it as your main evidence, a smart IO (rather than admit their error) may say that memo has already been superseded without showing you any proof of such a claim.