Austria Stamp Printing Error For $1

Hello I am a new member.

I have this stamp from Austria: Scott #P15, Mercury, 2h, dark blue. I have this stamp and when I compare with similar stamps there is a difference. My stamp has different numbers of dots in the right corner (the red circle). Because I have limited information, I look for information on the internet. I found this website but it is not free so I pay the subscription fee and the result is my stamp is printing error but it is not valuable only $1.

I am looking for another resource here, so what do you think of it?

There are no trusted stamp dealers where I live now. If it is valuable I will sell it to trusted stamp dealers. My choice is Stanley Gibbons.

You are much too hopeful, I think. It would cost you much more in postage to send that stamp to someone, than it will ever be worth. Besides being a common stamp, your example is in less than good condition.