That's not the case. I've had an extra pass since they were first issues in NY and I have three passes which we rotate between cars and only three of the cars are registered.
Something tells me this is not what you wanted to say. You have three passes that are rotated between cars and three cars are registered? That means all three of your cars are registered, so you should not have a problem.
From the MA EZ Pass FAQs (I have MA...I still have the old Fastlane transponder):
May I use / move my transponder from one vehicle to another vehicle?
Yes, the transponder may be used in another vehicle provided both of the following conditions are met:
- All vehicle license plate numbers in which you intend to use your transponder must be listed on your account.
- All vehicles which you use your transponder must be of the same class. For example, if you registered your transponder with a 2-axle, 4 tire vehicle with non-commercial license plates, you may only use that transponder with other 2-axle, 4 tire vehicles with non-commercial license plates listed on your account.
NOTE: Commercial license plates, including dealer plates and livery plates, are not permitted on individual accounts.
From the New York FAQs:
Do I have to set up a separate account for every car I own?
No,
each vehicle should be listed on your application. You may interchange your tag amongst your vehicles, provided they are the same vehicle class, or you may request a tag for each vehicle. Only 4 tags per account are allowed for individual accounts.
All that being said, different states appear to have different requirements. It would
probably definitely behoove the OP to take a pragmatic approach in obtaining a tag, especially if it is borrowed.