What logic is used to cause a cell in a drawing Title Block to be automatically locked?
Any cell containing more than one attribute, expression, or smart text will automatically be locked. This is because when using the Populate Title Block Dialog, the user may only enter one piece of information per cell; i.e. only one attribute or expression value can be entered in the Populate title block
Moreover a cell which contains system attribute such as sheet number, number of sheets will also be automatically locked as these attribute values cannot be modified.
Note that if a cell contains just one part attribute (which is not a system attribute) or just one expression then it will not be automatically locked.
The NX docs provide the following explanation note for Lock Status (automatic icon):
NX Help--> Design (CAD)--> Drafting--> Drawing Templates--> Basic drawing templates
Because you can enter only one piece of information per cell, any cell in a title block containing more than one attribute, expression, or other object is automatically locked.
Notes and References
OS Version: 1064