No, there are always small differences between the different ships of one class. In naval units, this is used to identify a specific ship with (at last in the past) people memorizing the differences from images.
Nothing substantiates that in regards to SF ships of the same class that leave construction yards.
Changes from ship to ship of the same class happen only because each crew customizes their own ship to their needs and their ideas as a result of personal experience in the past and the ones in the field.
If particular ideas results in a change that improves performance it will probably be incorporated class-wide (adapted for flee-wide use) ... and will become a standard for new ships of the same class that are constructed.
We are talking about fictional SF after all set 270 years into the future ... not reality.
Deks... just to put matters into perspective (and I'm not CHALLENGING you here... just askin')...
Would you mind telling us a little bit more about yourself? There are a number of folks who post regularly in this forum who have a massive amount of real-world knowledge about naval vessels (far more than I do... I'm an aerospace guy!).
You speak as though you believe you have a claim to being an "authority." Just to put matters into perspective, I'd personally like to know a little more about who you are. (and the same goes for the rest of you guys... except for those of you who I already know... but feel free to chime in for those here who DON'T know ya!)
Me, I'm a research and development engineer in the aerospace industry, though I've also worked for Emerson Electric, Ford, Maytag, and a couple of other you've never heard of throughout my career. I served in the military, but not in the Navy.