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| Tartan Name | Ontario, Northern | | | | Category | District
| | | | Designer | Teall/Smith | STA Ref | 956 | | Date Recorded | Not Specified | STWR Ref | 956 |
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| Tartan Name | Ontex | | | | Category | Corporate
| Reference | 11358 | | Designer | McCann/Urquhart | | | | Date Recorded | 03/09/2015 | | |
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| Tartan Name | Ooni Limited | | | | Category | Corporate
| Reference | 13649 | | Designer | Prickly Thistle Scotland Ltd | | | | Date Recorded | 11/10/2022 | | |
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| Tartan Name | Open Championship (1998) | | | | Category | Corporate
| | | | Designer | House of Edgar - Macnaughton Holdings Ltd. | STA Ref | 2575 | | Date Recorded | Not Specified | STWR Ref | 2575 |
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| Tartan Name | Open Championship, The | | | | Category | Corporate
| | | | Designer | Not Specified | STA Ref | none | | Date Recorded | Not Specified | STWR Ref | 2803 |
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| Tartan Name | Operation Encompass | | | | Category | Corporate
| Reference | 11951 | | Designer | Wilton, Brian | | | | Date Recorded | 19/10/2017 | | |
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| Tartan Name | Orange Fanaticos | | | | Category | Corporate
| Reference | 10105 | | Designer | Frankfort, David C | | | | Date Recorded | 23/11/2009 | | |
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| Tartan Name | Oranje Veld | | | | Category | Fashion
| Reference | 15322 | | Designer | International Tartans | | | | Date Recorded | 16/03/2026 | | |
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| Tartan Name | Order of Saint Lazarus | | | | Category | Corporate
| Reference | 11388 | | Designer | Ross/Waterton-Anderson | | | | Date Recorded | 14/10/2015 | | |
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| Tartan Name | Order of the Holy Sepulchre | | | | Category | Corporate
| | | | Designer | Kinsey, Ronald Stuart | STA Ref | 2161 | | Date Recorded | Not Specified | STWR Ref | 2161 |
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| Tartan Name | Order of Vitéz | | | | Category | Corporate
| Reference | 12652 | | Designer | Wilton, Brian | | | | Date Recorded | 21/10/2019 | | |
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| Tartan Name | Ordinariate, The | | | | Category | Corporate
| Reference | 12554 | | Designer | Black, Ruth | | | | Date Recorded | 09/07/2019 | | |
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| Tartan Name | Oregon State University | | | | Category | Corporate
| Reference | 10131 | | Designer | Lorenson, Krisja | | | | Date Recorded | 19/01/2010 | | |
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