I think Yama and Nissan combination are moreover generic names used, perhaps, by a corporate importer. I'd be checking for which Japanese company made the lugs and frame which if aluminum it would likely say so. While it appears like a high quality bike, those silver decals or more likely stickers, stickers kind of give it away as a lower priced import. Pretty much has everything ya might want, looks, style, and shifters in the bar ends. But something ya might have found at a large retail like Sears . Seems your parents got the right idea, checked the market, bikes shops and stuff and happened to find yours at a nice, lower price point. And, per your experience, did a good job at it too. Find that japan frame and you get your answers. IDK why b/c I know very little about imports but soon as I saw your photos, and silver , genetic stickers Nishiki bell keeps ringing. Yet, IDK why because, actually, i have no clue to base who did it. Regardless, concentrate in time range made, me dinks you'll find the actual maker, for its frame.