In this particular member's situation there was no activity in either October or November that triggered a statement. The credit union's quarterly (and year-end) statements are configured to produce a statement for every member, regardless of activity level, but monthly statements are more restrictive in an attempt to save postage costs, and not every member gets a statement every month.
NOTE: CU*BASE statements have a considerable number of configuration options that allow credit unions to produce member statements to meet their needs and to include the information desired. The first stage of producing statements is to determine who qualifies to get a statement. Based on the credit union's qualification criteria, monthly statements include members with a checking account, or a line of credit or loan. CU*BASE then makes the assumption that the member will be receiving a statement and updates a control date indicating such. However, there's an additional option later in the statement processing cycle that a CU can activate, directing the system not to send a monthly statement if there are no transactions. This basically eliminates the member from receiving the monthly statement that month, but there is no mechanism in the software to go back and reset the statement control date. This is how the CU*BASE statement processing works.
This member did have a checking account, and the credit union's statement settings say that all members with checking accounts normally qualify for a monthly statement, but only if there was activity on the checking account. So the system did evaluate that member in October and updated a control date on the membership to October 31. (This control date records the last period when statements were processed, even if that particular member didn't happen to get one.) Then again in November the control date was bumped forward to November 30. So as far as the membership showed, both October and November statements periods were completed. When December statements were produced the system took that control date, added one day and printed December 1 as the starting date of the statement period.
Coincidentally, this member actually did have activity during December, but he would have received the same statement, with the same date range at the top, even if there was no activity in December.
IMPORTANT NOTE: This particular member did have a checking account, which is the primary factor that decides whether he gets a monthly or a quarterly statement. Although this is controlled by the credit union's configuration, it is a very common setup based on Reg. E requirements. (Another setting that's common is to qualify members based on the presence of EFT transactions (ATM, Debit, etc.) on any account.) If this member had, say, only a regular savings account with just a couple of teller deposits and an inactive line of credit, he would have been bypassed altogether during the monthly statement routines in October and November, so the control date on his account would still have been sitting at the end of September. Then when the December statement was produced the date range would show as a true quarterly statement period, not a monthly period. So there are actually two configurations at play: account types that qualify a member to get a statement, and whether there is qualifying activity or not during the statement period.