| Company / factory era (the primary Standel dating frame) | 1953-present | 7 | Era only. Within the 1953-1967 window the amps cannot be dated further without component evidence — which is precisely why the serial number does not |
| Construction and cosmetic markers | 1953-1960s | 5 | Marker, not a date: it identifies the early hand-built series versus the later mass-market and solid-state amps. The first design covers about the fir |
| EIA component codes | 1950s-1970s | 0 | Component codes date the PART, not the amp: a replaced transformer/speaker/pot can be newer than the amp. Upper-bound rule — the amp is not older than |