I agree with Andrew completely.
That said, in answer to your question:
You could
Insert a Caption for each textbox. The numbering will depend on the placement of the captions not on the flow from one textbox to another.
The dialog above would place the caption in a separate textbox under the current one. That textbox could be moved to the left or right of the original. In the example I created a label of TB but no label would be required. The screenshot below shows the original textbox and the caption textbox both selected prior to grouping them.