Well done !
Quite possible then the number had no relevance to the silver content. I've found gold jewellery in boxes of costume jewellery before that had no hallmark on them. Usually the vendor has them back as soon as they find out !
On older jewellery, marks can often have been rubbed or polished off. You ladies - or gents, i guess ! - with any rings will know that.
829 is, quite literally, an odd number.