In Texas it's the County Tax Assessor-Collector, not the County Clerk, who serves as the State's Agent for processing motor vehicle registration and licensing matters. Most County Tax Assessor-Collectors in Texas have a good grasp of laws and procedures relating to all of these matters, and keep abreast of revisions.
The 'window clerks' (usually the County Clerk's staff) who actually interface with the public and day-in-day-out actually process the paperwork and collect the fees are another matter entirely IME. Some are consistently knowledgeable and diligent in their duties (taking care and time to ensure they understand the each of the documents evidencing purchase price, for example), while others are less diligent (or competent) for whatever reason(s).
I imagine there's nothing unique to Texas in any of this.
Personally, I find little joy when I encounter the latter even when that presents the possibility of a 'windfall' to my benefit in the case of a particular error (I try to point-out and correct those errors). IMO I, and all citizens, reap a much greater long-term benefit when the collection of taxes and fees is consistently and properly administered.
Just sayin' (one person's observations and opinions)