I really don't care how thing were in the past, but at present there are only 3 significant differences between NAR and TRA.
1.) NAR has a model rocket program and TRA does not.
2.) TRA allows it's members to make their own motors and NAR does not.
3.) NAR's print magazine is included in the membership cost.
Those are the only significant differences.
There are several minor differences between NAR and TRA, the most significant are:
1.) NAR insurance is universal, but AFAIK TRA insurance is only valid at TRA sanctioned launches within 1 mile of the launch pad.
2.) TRA has a high power mentoring program for junior members that allows participation in L1, L2 and L3 projects while NAR only permits junior members to participate in L1 projects.
As for commonality, reciprocity is nearly 100%.
1.) TRA members can participate in any NAR sanctioned launch to the level of their certification, however TRA members are limited to using certified commercial motors as NAR does not sanction research motor activities
2.) NAR members can participate in any TRA sanctioned launch, Commercial or Research, to the level of their certification, however NAR members are limited to using certified commercial motors.
3.) By federal law, minors can not be high power certified and consequently junior member high power participation programs are not reciprocal.
The number of high power certified individuals in NAR and TRA are within 10%, and many seniors have dual memberships, but NAR has about 45% more members. Today I attribute this to NAR's model rocketry programs which can be conducted from small urban and suburban parks and fields that are not large enough to support high power rocketry with is the primary focus of TRA.
Bob