Hi Charl,
The question is: have you had a overflight clearance in place at your numerous previous visits to Nam? If YES, then nothing have changed since.
If you didn't have a clearance in place, then you have just been lucky and so have many others. But, many other haven't been so lucky and as I have mentioned in my post, they were sent straight home. It all depends on the individual who potentially confronts you. If he/she knows their stuff, you are in trouble.
It might be that you can apply upon arrival but if you intend passing through a border post, then you are stuffed(sometimes

).
I'll enquire in any case about the rules and regs tomorrow and post soon after.
JJJ, you are more than welcome to contact me.
Keep well.
Hanno