The database I can access does not have any records visible prior to about 1999 or so. Somewhere in a cabinet in Japan is a metric-sized index card or manual logbook showing the exact date of manufacture for the serial number, but it is next to impossible for me to get that short of a subpoena. :wink:
The HS621 was first introduced to the USA market in about 1992, and this model was replaced by the HS724 around 1998.
Generally, the last six digits of the serial number indicate the running number of units manufactured (but not always). So this specific unit was probably snowblower #27,708 in the production run. This model was made in Japan, and sold in other markets (probably Japan and some parts of Europe) before being launched in the USA. So, the 27,000+ run was global, and not just units sold in the USA.
Honda issued two Service Bulletins for the HS621, but both applied to a range of serial numbers units made BEFORE 27708 so they don't apply. If anyone would like copies, drop me a PM with your email and I can get you a .PDF copy (FYI, the bulletins, #5 and #6, covered a minor modification of the retaining clips that hold on the discharge chute (it may come loose), and an updated & more durable auger housing assembly for units with broken auger shafts.) There were never any Safety Recalls or Updates for any HS621.
Skimming the parts catalog, most parts are still available, with a few completely gone forever, including about half the recoil starter parts:
A paper shop manual is available from Honda via eBay or Amazon (free shipping and updates for 3 years...); here are the links:
Amazon.com: Honda HS521 HS621 Snow Blow Throw Service Repair Shop Manual: Patio, Lawn & Garden
Honda HS521 HS621 Snow Blow Throw Service Repair Shop Manual | eBay
Finally, there were never any accessories or optional kits for the HS621 (like a worklight, drift breaker, etc.).