Hi - There should be a serial number on the plate - it may be possible to work out exactly when the bass was made from that number.
However, a quick squizz at at some Japanese Greco catalogues tells us that your bass is a PB750N:
http://psyco.jp/greco/p/c03_07.jpg
Which first shows up in 1975 & seems to run through to 1977 before disappearing.
Greco is predominantly a Japanese domestic brand, your bass is possibly quite rare outside Japan, and may not have been officially exported if it doesn't appear in English-language promo material.
Yours looks in great condition for a 30+ year-old bass - look after it! 
 
Jon.