How can I determine model number and year on a Colnago Dream B-Stay?

Bicycle frames have serial numbers, not model numbers. Since you seem to be building up a frame, the term "model number" cannot apply. The date of manufacture of a frame can be determined by finding the serial number that is somewhere on the frame and asking the manufacturer

Thanks , I only ask because in my previous thread trying to figure out what size bottom bracket to use I was told they couldn't be sure without model number..... Pretty sure all Colnago BB are the same aren't they?

Which bottom bracket you should use has very little to do with a frame serial number. Your frame will have a certain bottom bracket shell width and will have a specific threading, likely Italian, or possibly English. Once you have determined that, the actual bottom bracket you use will depend on the crank you plan on using. Your other post states that you wish to use an ISIS bottom bracket, this implies that you have a crank that requires an ISIS bottom bracket.

FSA Isis drive Pro Carbon crankset.... Don't think Colnago makes anything but Italian thread.... Which means it's a 70..... But 108mm or 118mm

Sometimes it is just trial and error. Axle length is dependent on the crank. So unless someone has the same frame and crank you just have to take a best guess. My guess 108, Italian thread. 118 is getting into triple crankset territory.

Hopefully someone else will confirm this.

The crank will determine the length of the spindle you need

This says 108. I'd expect 118 to be for triple ranks,
FSA Carbon Pro Elite Compact Cranksets Reviews - RoadbikeReview.com