Land-survey-taxes issue.
If the accepted boundry was in error and their surveyor corrected the error, you have not been paying taxes on that portion of property any how. Let me explain.
Your lot size by deed says (pick a number) is 200' wide by 200' deep, with 200' of road frontage. However when you built your fence you missed the line by 5' so now you are 205' wide. How ever the paperwork that the tax man holds say 200'. They do not survey everyones lot, they look at the deed make the ass. and you pay. Now on the other hand the neighbors have been paying taxes on five foot of property that you have taken control of.
If the surveyor was/is a state liscensed surveyor he would be a fool to knowingly mark a boundry wrong, he could face a fine, lose his liscense, and reputation. All over a small strip of property that holds no value to him. You think your neighbors bribed him? Just how much do you think a narrow strip like that is worth? Unless it's in downtown Manhatten noway would it be worth the amount needed to bribe the surveyor. No selfrespecting surveyor that makes a living as such, would move a line for a $100 bribe. Talk about ignorant, lose your living for $100 or even a $1000 bribe.
I suspect maybe just maybe the line may have "slipped" one way or the ther over the years. I worked as a rodman with a survey team for a number of years and we'd see that type of thing all the time. Some one begins cutting grass along the edge of the property moves over a little bit every year, the next owners of the property accept that the previous owner only cut his own property. Or: They plant a row of bushes along the property line but because they want control over the bushes they plant them 3' inside the boundry. Years later some one removes the bushes, every one assumes the base of the bushes is/was the line, but the line is actually 3' on the far side of the base. Believe you me you see this type of thing all the time.