The overall length of a rib is usually from bow to the stern of the boat. This is usually used in Marinas (to calculate the cost of mooring etc, and they also include the tilted outboard as well).
But as for retubing, they mainly care about the langth of your "Hull" not your Tubes. your rib may have extended rear buoyancy tubes and they should be included in measuring the overall length of the tubes.
if you want to get a quote, take a photo of your rib and then write the measurements on it (use microsoft paint or something like that). Have a look at this:
They need all those measurements to quote you. Also, measure your draft.