In the “for-what-it’s-worth” department, I did a Google search on 21MAY2012, all languages, for the following:
“panem nostrum supersubstantialem” 148,000 hits
“panem nostrum cotidianum” 147,000 hits
“panem nostrum quotidianum” 111,000 hits
“panem nostrum super-substantiale” 6 hits
“panem nostrum supersubstantiale” 1 hit
How to interpret that? I don’t know. Both “cotidianum” and “quotidianum” sound close to the English word “quotidian,” which is a highbrow English word for “daily.” Combined figures for those two words (“cotidianum” and “quotidianum”) outnumber “supersubstantialem” hits by 75%. I imagine old music, written in Latin, isn’t going to change to “supersubstantialem” because it just doesn’t roll off the tongue easily!

The Holy See’s website further muddles things because as my previous post stated, the Catechism of the Catholic Church employs both “cotidianum” and “super-substantiale” (sic) for the Lord’s prayer, and then the current Vulgate employs both “supersubstantialem” (in Matthew) and “cotidianum” (in Luke) for the Lord’s prayer.
– In Christ Jesus Through Mary, Scott Ramsay