421 is the code for Saddle leather in '69. Depending on WHEN your '68 was assembled, it could very well have been ordered/built with the 421 interior color. Whoever did the appraisal was wrong to deduct on the value of the car just for that reason....possibly, he/she needs to do a little more homework.

What is the build date of your car?

Not that it helps you any but my Black Book(2001 edition) lists the 420(saddle vinyl) and 421(saddle leather) for 65-67 in addition to 69.

My books all say they are '69 codes, but not '68. You are going to have to check the trim tag pretty closely, make sure it hasn't been replaced. If it is a VERY late '68, like an "L" code (July), it could possibly have a '69 code. '69 production started in August. 

Thanks,  The VIN # indicates that it was msde in January.

The VIN number ends in 410007, which makes it a January build.

Well...that doesn't exactly put it as a late build! However, the interior colors were subject to changes, if they were ordered by the customer/dealer. If a particular color was requested, but not "available" for that year, it could be had, if ordered thru the correct channels, such as GM sales/management/design etc. The car may have originally been ordered by a GM employee...who knows? The only way to verify what it had from the factory would be to have the original window sticker, or the tank build sheet, which MAY still be on the car.
As others have suggested, the trim tag may have been changed, also, but the date code on it would tell the tale, unless it is a reproduction tag, made specifically for the car.
Does the trim tag date agree with the VIN build date of January '68?Adams' Apple2008-09-08 04:57:20

F25 = 25th day of the month...Don't have the info here with me, but, if production started in Sept '67, then F would mean Feb 68...apparently, your car's VIN puts it as a Jan built car...NOT GOOD!
Looks like someone has changed the Trim tag...

(unless my Texas math is wrong) Annnnd...apparently, it is! Adams' Apple2008-09-09 18:33:05

Is it possible 68 production "started" in August 67 even tho none were apparently built in August? 1967 production ended in July. Probably a major line changeover took place.