Well this is why when we do Hunter Ed and CFSC courses I make it a point to tell everyone that they should not remove the plug and if they buy a new or used semi or pump to check that the plug is in place. Even here in NS people have been charged thinking that their shotguns met the Federal Migratory regulations when hunting ducks or geese only to learn that their firearms upon inspection did not.
I had a former student call me about 3 yrs ago, he was given a warning he was hunting grouse and woodcock the plug was missing from his father's old wingmaster.The CO at that time said the chances for a conviction were slim and he would not want to see a young hunter who was not trying to break any laws get in trouble. The CO had no problem with the plug not being in the gun if only Grouse or other NS small game were being hunted the problem as was explained to me was Woodcock being Migratory and the regulations surrounding the number of shells permitted.
So as many of you have stated do not remove the plug and if not sure check to see and replace the plug if needed. In NS and no doubt other places the Federal Migratory Regs do not always mirror the provincial regs and vice versa. A popular pheasant area down in the valley is Bellise Marsh it is also a regulated Federal Migratory bird area all hunting there must meet the Federal Regulations for non toxic shot and the carrying capacity for shotguns. There is a section in our regulation booklet that points this out. This is one of many reasons I tell people to read that booklet every year and like it or not the day is coming when for hunting small game in NS non toxic shot will be required if for no other reason then it aligns itself with the Federal Migratory Regulations.