You need to find out what your TT came with as standard equipment - what was built into the base price.
Examples:
If there were two refers available, then the smaller one was standard equipment. Don't price it in as an extra unless it is the larger refer that the original owner had to pay extra for.
There may have been two sizes of air conditioners available. The 13.5 would have been standard equipment. If there was a 15K also, then it was probably at extra cost.
Was the awning standard or did they have to pay extra for it.
The stove top is always standard and the oven usually is also, but you need to know if the oven was standard or not.
Maybe two size of tires or axles were available.
Maybe one vs two batteries.
Maybe two sizes of furnaces.
Get the idea - the base NADA price covers all of the standard features. You can only add in the price of the extras if extra was paid for them. Someplace in one of the cupboards there was a build sheet showing you what was standard equipment. Hopefully it's still there some place.
Bill