I use multiple layouts to produce build drawings and I use the name of the layout tab to identify the sheet on the shop floor.
I currently use a field in the titleblock that calls the system variable ctab, the problem is that whenever you update the fields, they all change to the name of the current tab, not the name of their own tab (by default, when you open the drawing, they all say Model).
I resort to building all of the layouts and converting that field to text prior to printing.
I'm looking to save a potentially confusing if missed step.
Check the variable FIELDEVAL is 31, unless you have a reason to set it differently, fields should update before a layout plots. I use the same CTAB in my drawing titles without problem.