...the "other valuable items" is probably the key word. I'm very careful on the customs declarations to clearly write "used Timex watch". Hey...maybe the customs/postal authorities automatically assume that if it says "Timex" it can't possibly be valuable...ha ha ha. Well, if that's the case, GREAT.
Finding, reading and understanding the "fine print" in customs/postal regulations is extremely elusive. I know for a fact that both Spain and Italy clearly state that "watches" along with jewelry are prohibited items. For several years I was still able to mail watches to both countries with no difficulty then they suddenly started seizing and taxing my watches. These were just plain old vintage Timex watches. My thoughts are that the "prohibited items" clauses in the regulations are rarely enforced. But, one thing's certain. If a watch is lost or damaged there's little or no chance of making a claim against the postal insurance if the item that was mailed was a "prohibited" item.
I had that happen to me. A watch that I mailed to the Balearic Islands (Mediterranean Sea) was lost in the mail. I had mailed it via Registered Mail with Insurance. Supposedly this was the Safest, Most Secure method available requiring the signature of every person who handled the package from my hands to the hands of the customer. It was also among the most expensive methods of mailing. When I filed my insurance claim with the U.S. Postal Service it was denied because the item I mailed was a "prohibited item" which just happened to have been a used/restored vintage Timex watch. They never once mentioned the prohibited nature of the watch when I had declared it on the Customs Declaration when I mailed it.