Eros was a brand name owned by UK importer/distributor Rosetti. There was also an Italian brand E-Ros, which predominantly produced acoustics and has an association with Eko. These two brands are not connected.
Some Eros guitars were Matsumoku-made, if we now accept that the Steel Adjustable Neck plates were exclusive to Mat. My earliest posts on here were concerning an Eros Mk II Lp copy I had:
viewtopic.php?f=19&t=3021Pics are sadly long-gone but it was this:
I also had an Eros Tele copy - it's a Fujigen, absolutely identical to the early versions of the Ibanez 2352 Tele copy:
Recently a few Eros-brand LP copies have been turning up on UK Ebay - I think these are later instruments and I'd be prepared to bet they're Korean-made, not MIJ. There 's one on at the moment, I can't post a link here but this is the item number: 190434897249. This has all the hallmarks of low-end late 70s MIK stuff, and I think Rosetti shifted to suppliers outside Japan the way a lot of brand owners seemed to after about 1976.
Obviously without pics it's impossible to say whether or not the guitar the OP's interested in is a Matsumoku, or Japanese - but in this instance I'd go with the notion that if it doesn't have "Made In Japan" on the neckplate then it isn't - and absolutely isn't a Matsumoku.
Jon.