Two different cars, why is that.
From what I know that the Blue Badge is issued personally. (Apart from Organisation Blue Badges)
We have two cars parked on the same street. It's a public parking with a lot of other cars. I reported my blue badge lost and was issued a new one. I found the old one and therefore had two. The old and new one. The old one, which had been cancelled due to being reported as missing, was issued with a PCN and reported to the council. Council now want to interview me under caution. I hope this helps clear up your question.
It seems like you are banged to rights.
Under the legislation and in Blue Badge booklet the badge can be only used in 2 situations.
1. A driver who is a Blue Badge holder is allowed to display the badge when parking.
2. A passenger who is a Blue Badge holder who has been getting in or out of a vehicle is allowed to display Blue Badge while the vehicle is parked.
At the back of the Badge there is a clear condition that it says if the badge is found it should be returned to the local authority.
As you have mislead the local authority and I would not be surprised if they prosecute you for fraud. If you are convicted of fraud and you would have to declare to insurance companies including car and home insurances, etc.