OK I think you need to load stock data. When I did this on your MYNN file the number of taxi signs went up for 79 to 167. This small image shows four signs in two pairs in slightly different locations. Each pair represents a sign from your bgl file and one from the v4 stock file.
One of the pair at the top is on the taxiway and may be a stock sign. You either need to delete all the signs you have in the original file which I don't recommend or delete the stock signs.
As it happens we are working on an update to make identifying stock items easier since what you have here happens in spades in P3D v5. This is becasue LM recompiled all the airports with new objects and updated layouts.
Give me 48 hours to finish the update and we will see where we go