I checked with our Queen of Serial Numbers, and she tells me Honda only has access to records of units built in the last 10 years or so. That is when they moved to an SAP-type inventory control system. Even then, not every single unit is fully documented with a "birthday" value in its record. Now they do have what's known as a Model Chronology, which lists out when models were first released and in some cases, when they were discontinued. The closest this data get is by year. So, in the case of the HR214, it was first built in 1984, and discontinued in 1989, when the HR215 was introduced.
Hope this helps.
Caveat: I work for Honda, but the preceding was my opinion alone.