since 2010 i've been using piwik and got used that every month 2 tables are created
prefix_archive_numeric_2014_11 & prefix_archive_blob_2014_11 weren't created this month
i'm using the latest version of piwik
i'm a missing an important change in piwik ?
Piwik should still create the monthly archive tables. do you see any error in the mysql error log? maybe you've reached some limit and an error is logged?
sorry for the delayed answer
i thought it should be created on the first day of the month, right after i visit the dashboard, but it didn't, however now was created
please mark it as invalid or not a bug :)