My experience is if it looks good and matches in the end they cant tell it isn't factory.
In the first 3 months I owned my TT we cut the bumper off Engineered a back rack welded to the frame and then added the rear bumper back on looks like factory welds (maybe better) and fits like a glove to the trailer.
Under warranty, its been to 3 dealers so far and one was the purchasing dealer and they all thought it was a factory add on.
My point is there are so many changes between years and manufacturers and factory add ons that the dealers cant remember them all and without looking up the bill of sale or contacting the manufacturer with the vin and then going through it with a fine tooth comb they just don't know. Not to mention their interested in getting you into a new one.
By the way looks good.