Why the Structure of measure's Master change each time

[Gery]

I have two Queries regarding Promoting interoperability performance category.

1)  in 2018 there was an attribute "substitutes" from where we identify the relations of the measures , but in 2019 the same attribute is there But BLANK.

2018: https://raw.githubusercontent.com/CMSgov/qpp-measures-data/master/measures/2018/measures-data.json

2019: https://raw.githubusercontent.com/CMSgov/qpp-measures-data/master/measures/2019/measures-data.json

2) How to identify the linking between main measure and it's Low volume.

for example : the main measure  EP_1 have an exclusion measure PI_LVPP_1 .