It goes along with teh special mid-battle retreat that FIGs can do, and also the fact that they can NOT remain in a combat zone after a batle (except by landign on an AC after a naval battle).
You HAVE to be able to MOVE in NCM to land in every type of battle EXCEPT a Naval Battle, and then you can ONLY stay there if you WIN.
If your side owns Panama at the START of your move (just before you do “purchase units”) then you can use it. The same is true for Suez if your side controls BOTH T-J and Egypt.
If your side does NOT control both sides at the time you purchase units, you cannot traverse Suez at any time during your move.
