As per https://github.com/cu-mkp/m-k-manuscript-data/commit/5cae31a667ab90a5474f186b43607aa3d3f40a31 commit, it appears that <ar> tags were added on a number of folios in the tc and tcn only (not tl).
The only words affected appear to be "garde(s)" and "cuirasse(s)" - perhaps this was a by-product of a bulk search/replace campaign?
appears to be a vestige of potential updates to markup related to arms vs. armor. These are getting <wp>