Stu has an unusual ability and skill, some what rare on the internet. Most all his information is correct.
You undoubtedly referenced the OP to that article on coaxial cable to illustrate the fact that coaxial cable length is not relevant in an RF transmission line.
Again this is true.
the co-ax feed line in a NGP (no ground plane antenna) is not a transmission line in this application.
The shield of the co-ax is a tuned element and directly related to the length of the antenna whip. The whip is not electronically interchangeable
with any type of ground plane antenna.
The cable and antenna are sold as a pre-tuned unit and neither element can be altered and still operate as intended. This means that the co-axial cable can not be extended from the length originally supplied.
Also may be helpful to know that while a NGP antenna may
give acceptable VSWR readings, it will, at best, give 20% less performance in transmitting and less obviously degraded reception. This is usually accepted as a fair trade given the alternatives.