On 21 May, the source wrote (citation (pdf)):

Exposition of the Transition from Thailand Standard Industrial Classification of All Economic Activities (TSIC) 2001 to TSIC 2009 on Quarterly Gross Domestic Product (QGDP), Production side

At present, Thailand’s economic activities within the production boundary comply with Thailand Standard Industrial Classification of All Economic Activities 2001 (TSIC 2001) [which is] based on the International Standard Industrial Classification of All Economic Activities Revision 3 (1990) of the United Nations (UN) (ISIC Rev.3, 1990) and has been used in QGDP compilation since 2002.

At present, the Department of Employment has improved the classification of economic activities of Thailand to be consistent with ISIC Rev. 4 (2008). The new classification is called TSIC 2009. [...] The NESDC has improved the calculation of the Annual Gross Domestic Product (GDP) according to the new classification (TSIC 2009), published it since 2015 and also revised the historical data from 1990 to 2015 [...]

[...]  the NESDC has planned to announce the QGDP based on TSIC 2009 in First Quarter 2019.

In response, we have:

1. Archived the predecessor (TSIC 2001, reported 1993Q1 to 2018Q4) by renaming with an "_I3" specifier, by marking their metadata as "discontinued", and by segregating in the catalog.
2. Created one-for-one replacements (TSIC 2009), which have an unchanged start date.

Active dataset properties:

• Classification: TSIC 2009, derived from UN ISIC Rev. 4
• Measurement: Millions of Thai baht at current prices (Mil. THB) or chained year-2002 prices (Mil. Ch. 2002 THB)
• Adjustment: Seasonally adjusted (SA) or not (NSA)
• Geo coverage: Country
• Native frequency: Quarterly
• Start date: Uniformly 1993Q1

The series reside in the historical catalog (Thailand » National Accounts » by Value Add » Quarterly) and are:

• NALSGDPTXAF_I3UQ.ITHA = [DISCONTINUED] Non - agriculture, (Mil. THB, NSA)
• NALSGDPTXAFUQ.ITHA    = Non-agriculture, (Mil. THB, NSA)
• NAHSGDPT_I3AQ.ITHA    = [DISCONTINUED] National accounts: production approach - Gross domestic product - All industries total, (Mil. Ch. 2002 THB, SA)
• NAHSGDPTUQ.ITHA       = National accounts: Production approach - Gross domestic product [real GDP], (Mil. Ch. 2002 THB, NSA)

Because catalog locations are subject to change, the upper-right search box on DataBuffet.com provides a "find in catalog" that accepts a mnemonic.