These works, known only through their inclusion in Haydn's Entwurf-Katalog, are identifiable solely by their opening themes, which are known through their incipits.

Although these works were previously known, neither Päsler nor Hoboken included them in their sonata numbering, as their scores were not extant. However, C. Landon incorporated them into his numbering as works that existed at the time.

The Vienna Urtext Edition, by adding these eight works—Nos. 21 to 27, and the incomplete No. 28—brought the total number of sonatas to 62.

List of Sonatas

• No. 21 D minor Hob.XVI:2a
• No. 22 A major Hob.XVI:2b
• No. 23 B major Hob.XVI:2c
• No. 24 B-flat major Hob.XVI:2d
• No. 25 E minor Hob.XVI:2e
• No. 26 C major Hob.XVI:2g
• No. 27 A major Hob.XVI:2h
• No. 28 D major Hob.XVI:5

See also Composer's commentary not found?