Like most options, ECLs differ based on other equipment. There are no RPO ECLs specific to COPO 9560 & 9561. When they did the query looking for M22 ECLs specific to BB it picked up all of them including COPOs. When the report was summarized it was assumed all 867 were for L78s.
But when they queried for L78 ECLs could it have picked up COPOs? As I stated L78 is always listed on Canadian COPO docs. There is one out there at this time:http://www.yenko.net/ubbthreads/ubbthreads.php/topics/688190/re-yellow-rs-copo#Post688190
As usual L78 is listed along with all the other equipment. But there are no ECLs shown. Maybe 20 years ago when you requested build info on a Canadian delivered car they just copied the page your VIN was on along with 18-20 others. I have a few of these and looked up the COPOs. All of the COPOs I can read also list L78AA5 along with 9560 or 9561.
If they did the ECL query using the same info from the shipping reports I have to say there is a possibility the 4,889 L78 build total included COPOs.