Konami didn't ditch MSX after 1990. According to MSX FAN 1991-07 page 100, MSX FAN redactors desperately needed 7 Pennant Race 2 for their contest and were overjoyed to find new stocks but nevertheless found it odd 3 years after the release, and called Konami "which had not been in contact lately" (= MSX FAN too thought Konami ditched MSX) then Konami answered recently rereleasing Parodius/Pennant Race 2/Gradius 2/F1 Spirit.
It might had been a tip of iceberg given MSX FAN noticed it by coincidence. Some packages look too new to be from 80s. While package and rom designs likely remained unchanged, the bulk mail stamp due date is the identifier. The stamp section at upper left corner of the enclosed user registration postcard indicates it in year-month-day format with the year in gengou so a pre-1989 postcard says Showa 6* while a later one says Heisei 1/2/... The due date is usually a year from the shipment, so if the year number is 4 (=AD 1992) or greater the package was 1991 or newer.
Dear owners, would you mind looking at the enclosed postcard and report if the first figure in the stamp section is <59 and >3?