Hi Cerjak,
Il faut faire la difference
Fernando K is an expert and fernando (without K) is only a small curious collector
The Bustuindi with a rampart lion is Juan Esteban, an outstanding smith, mentioned as so by Jovellanos when he visited his home in 1791 (quote Lavin).
The other two marks (UBARRA? and GVU..S) are not listed in Lavin's book, neither within my reach.
Maybe Fernando K can trace them.