Considering the numbers of your single part elements, I presume the method used to number is : With drawing number. This method use the drawing number to give a part mark to the object detailed on it. Due to this, using this method is not possible to give another number to an object if the drawing number of dwg file remains the same. Once created, a drawing can't have its drawing number changed, therefore using this method, you can't change a part mark for an object without recreating the detail drawing.
By default, when detailing starts on a new model, the first number used is 1. But, you can change this by modifying the following default : Start number for drawing numbers. Defaults can be found in Management Tools / Defaults category. After changing the value of any of them, you need to press on : "Load settings in Advance" button to apply the modification to the current AS session.
For example, in your case : you remove the numbering. Then, delete the drawings. Modify the default to match the new start number for your drawings / part marks (to 31 to follow your example). Create new drawings - the start number will now be 31, and the elements will take this number accordingly.