Hi and welcome Matt. I've not used mine yet so have thought about a lot of the same questions as you.
I have no idea how you date them - I guess based on serial number , but my older smaller bombards had a date on the transom plate...but not on the one I have now.
I dont 'think' the design has changed , but am not 100% sure , but red is normal grey I have only ever seen one on ebay....
Nasher is your man for patches , but if done properly/well I dont think would be a concern.
When everyone is sorted we shall have to arrange a cruise - Me , Nasher , JK, you... any others ?