So it was you!!!
I have one post where they must have dumped the last half load around the post. The concrete is about 3 feet across and god knows how deep as I have never found the bottom. I put the spur in by chiselling a hole into the concrete and leaving most of it there.
The others I just split the concrete with a sledge, removed half and dropped the spur in.
You don't need to replace the posts as they will last another 20 years once bolted on. You also don't have to disturb the fence either as you would to fit one of those hammer in fixings that rust away after five years. They may be quicker but they are not the best.