Missing Strongholds

I created a world in Single Player, and while I do not remember what version it was on, it was recent enough (this calendar year), it was likely 1.11.
I downloaded the Server and copied the 'world' data over, started the server and had a friend join.
When attempting to find a Stronghold, the output of the /locate command on the console does not have a Stronghold there. The old single player world and the server have two different seeds (unsure if this is expected) despite a direct copy of the folder. Using some online utilities I have checked multiple Stronghold coordinates for both the single player seed and the server seed to no avail. I have checked 4+ different suspected coordinates for Strongholds, nothing.
I'm sure I'm missing something here, but I would like some guidance as to 1) What happened and 2) How do I find Strongholds now as the players are nearing that point.