When you add or delete data in column L, list N will automatically update accordingly
First, select the data area on a single column, then on the Insert tab, select the Table icon from the Tables group, in the create Table window, check the check box before My table has the headers and click OK . Then this entire data has been converted into a table. Now select any blank box then go to the Data tab and click on Data Validation as above, but in the Settings tab , for Allow you have to select List , click on Soucre box and the data zone is created. Click OK , the newly created list will look like you used the Filter feature.