Something that should be mentioned here:

CLR did clean the number tags really well. But it was a process of soaking for a while and rubbing them for a while then repeat.

But then I remembered the smal ultrasonic cleaner I have. Purchased it off Ebay for $20 a few years ago. I used it the clean automobile fuel injectors.

Putting the tags in the ultrasonic cleaner with some Evaporust cleaned them really well in about three cycles (maybe 10 min).

That is the route I would recommend to others.

It is a small cleaner unit that you would put jewerly in for cleaning. The tub in it is stainless steel though so you can use them by putting CLR, Evapo or brake cleaner in it and let her rip.