Depending upon condition, $400 to $650
You will have to contact Miroku to find out.
No published sn data I know of
The letters NZ in the serial number indicate that your Miroku made Browning was made in the year 1991.
No way to tell from just the serial number.
The Miroku shotguns will typically bring 80% of the value of a Browning Citori in similar condition.
In like "new condition", expect to pay around $1000 in a retail store.
I can't give you a clear answer if Miroku made the shotgun or not. However, may I offer a comment. Miroku has made shotguns for 150 years. From all I can gather, they are a high integrity organization and have made high quality guns for companies like Ithica, SKB,Weatherby,Charles Daly and Winchester. If you have a gun made by Miroku, I don't care what company has its name on it, you have a fine gun. Excellent design, fits and finishes. Durable and dependable. Sleek and good traditional looks. Good hunting.
The value of your miroku will depend on grade and contition would range from about 750 to 1200