Going back to the "collapsed" idea.
It could also refer to when a grave had collapsed when it was dug for burial , maybe the land in that particular churchyard was prone to that and possibly a system was put in place to worn future gravediggers of past problems.
Bit of a long shot , but i work in a Cemetery , and that sort of thing IS put in our burial registers , not with that particular abbreviation though.
Just a thought............. 
As I`m sure you are aware graves do collapse, mainly due to either a lack of time following the adjacent burial, a period of inclement weather &/or unstable ground.
Generally I`ve seen an annotation referring to a grave collapse with additional info such as "Grave collapse, not to be used for 1 - 2 years".
Use of grave shoring can help prevent collapse, but not completely prevent a collapse.
Interesting argument, but I`d like to see if the OP could get some more info from the Cemetery to help clear things up & thus help all of us to gain knowledge.
Kind regards
Steve
