After 1891, for sure, when the Belgians changed the ELG over star to crown over ELG and star. The pinfire cartridge ignition system is long obsolete, since the late 1800's.
J B Ronge et Fils, of Liége Belgium, was active between the 1880's and 90's. His main product was the cheap 'Bulldog' style revolver in .320, .380 and .450 calibres. Although there is a possibility that Ronge produced up to 600 revolvers for the Danish Navy, namely the 9x17 model of 1891, that may have been a one-off effort, as his subsequent products are of very low quality by comparison with any service arm.
Ronge was really a trade house, making and selling his cheap guns all over Europe to retailers who then put their names on his products, mostly very odd by our standards. One of his .32cal revolvers was called the 'Kobold', a kind of mythical underworld dwarf.
My reference states the Belgian ELG crown proofmark started in 1893.
Your plated Beligian pinfire's proofmark, without the crown, was used from 1811 to 1893.
The pinfire was the first successful metallic cartridge revolver. Several thousand large 12mm pinfires saw service in the American Civil War. Their heyday was from the mid 1850s to the 1870s. I believe yours is one of the later ones.