Over training does not increase strength or build muscle it does the exact opposite.
If you feel you want to do core work everyday don't work the same plane of muscles each time. Work rectus abdominis one day, work external obliques another day, work deep core muscles another day. Yes to a degree there's going to be rollover where one group of core muscles may get worked slightly but work different exercises to hit different parts of your core. If done logically I don't see an issue with knocking out a few sets everyday.
Personally I don't do any ab exercises whatsoever and I maintain a very solid six pack year-round.
Core work happens during most exercises if done correctly (other than on a machine) so I don't waste any time doing ab exercises directly . The only thing that I do core wise is lower back exercises to strengthen the Erectors. And no that's not accomplished through jelqing