| Thiers-Issard — tang stamp, lines and continuity (1884 → the present day) | 1884 → the present day (several generations of owners, from 1985 — Reynewaeter) | 6 | There are no exact years for the stamps; there is a confirmed founding date (1884) and a list of owners with years. For dating a specific razor no sou |
| Country mark (lower bound, NOT a year) | the requirement applies from 1 March 1891 (Tariff Act of 1890, also known as the McKinley Tariff) | 2 | A country mark is only a LOWER BOUND (the item is no earlier than the introduction of the marking) and never a year. For French razors exported to the |
| Grind, spine, scales, etching — era markers of a straight razor | 1700s → mid-1900s | 16 | Shared layer for all straight razors: it does not date precisely, but it cuts off an era. All rows are printed wordings from a shop-page guide review |