Many tables in the Derby documentation appear abruptly, with conceptual prose followed immediately by a table (with or without a title). Here are some examples:
There is no specific accessibility requirement that tables be properly introduced, but many companies' technical writing style guides require or strongly recommend it. Moreover, the WCAG guidelines have the following statements (http://www.w3.org/TR/WCAG10/#context-and-orientation):
"Content developers should make content understandable and navigable. This includes not only making the language clear and simple, but also providing understandable mechanisms for navigating within and between pages. Providing navigation tools and orientation information in pages will maximize accessibility and usability. ... The theme of making content understandable and navigable is addressed primarily in guidelines 12 to 14."
Therefore, in the interest of accessibility, each table should be introduced with some indication that a table is coming.
Further details will be provided in comments.