Well I'm the person who broke the continuity, and in retrospect it was a small mistake for me to do that.  Just to warn you, because of the ambiguity the road classification system it is fairly contentious.  It's weighs lane counts, what it links, speed and how much traffic is on it.  And different people have different weights on each.  

For instance, there's a road, "Irish Spring Road" over in Roxbury has been classified as almost everything in it's history.

One of my rule of thumbs was anything with a 30 mph and over speed limit would be tertiary at least.  

Regarding source:ref, OSM has a ton of mildly esoteric tags (and they keep making new ones) that ID doesn't show you.  I don't blame people for not knowing them.  But at OSM scale the more common ones are useful to learn.