yes you was right but it is 17 nodes to prevent a fork not 17 nodes to initiate a fork. 17 is what comes next to 2n + 1 which is basically >75%. 16 (or more correct 15,75) nodes is 75% and since there is no 1% of a node it needs 17 nodes for honest majority.
So over 1/3 is capable of initiate a majority fork. As long as it is up to 1/3 it is only a minority-fork which will die quickly.
Up to 1⁄3 of the nodes can be malicious or malfunction and create a minority fork. In this case the minority fork will only produce one block every 9 seconds while the majority fork will produce 2 blocks every 9 seconds. Once again, the honest 2⁄3 majority will always be longer than the minority.
Larimer 2017 dPOS the missing Whitepaper
The confusing part is that forking in dPOS is not the same as in Bitcoin. If we want to be free we could easily set up a new independent system, but as you have mentioned, this is not how things are intended. The best way realy is to re-elect. dPOS can be compromised by a 1/3 + 1 "Majority" but it will still run in a pending state, so that we only need to concentrate our stake to the running/remaining honest nodes.
Imma keep my eyes peeled @lauch3d! Thanks for the primer. I'd probably never have understood how this worked without your help.
Thanks!