I am in the market for a Curado DC reel. Lack of availability has lead me to look on eBay. A lot of the different ads on there say this reel is a 2018 or 2019 model or something like that. First off, how do you tell from looking at the reel what the production year is? Secondly is there ANY difference in the model made it 2018 vs 2019 or something?

I don't think they have an updated or newer model on the CuradoDC reel.  The schematics and parts are all the same and unchanged.  Shimano will usually note the parts on their parts website by giving an updated part number in their charts.  

 

As far as finding one on eBay.... you might look at Asian Portal in Japan.  I have ordered a couple of reels from them and have had great service.  The will not have the Curado though but they will have the Scorpion DC.  You can google it and find all sorts of info on it.