If we use the supraspinatus tendon as a specific example I think the following.
An intrasubstance tear is any tear of the SST which does not communicate with either the bursa or the joint space directly so it specifically relates to the location of the tear and not the shape. I am happy to use interstitial in the same setting, however I prefer to use intrasubstance for the SST
A delamination tear is a tear which is splitting along the length of the tendon and may “delaminate” right back to the MTJ in some cases. A delimitation tear may be intrasubstance but this is not necessarily always the case. I would be happy to use the word longitudinal split interchangeably with delimitation although I tend to use the word delimitation for the SST and longitudinal split for tendons with a simple longitudinal design like tibialis posterior or peroneus brevis, Remember that the SST has 5 discreet layers and I think of delaminations as happening between these layers whereas the tib post and peroneus brevis are much simpler and simply split along the length of the fibres.
I have attached an example schematic of an intrasubstance / interstitial tear,