An isolated lakkhangyao would also be transliterated by a small letter "i" with stroke (ɨ), but such should not occur in Thai, Pāli, or Sanskrit.
Note that paiyannoi, angkhandiao and angkhankhu (๚) are transliterated by the letters used for click consonants, not by double dagger, vertical bars or dandas.
The standard specifies the transliterations in code points, but someone working from this free explanation could easily deduce that the spacing forms of the tone accents should be used.
The ICU implementation, recorded in Version 1.4.1 of the Common Locale Data Repository sponsored by Unicode,[1] uses a prime instead of a horn in the transliteration of consonants.
This affects the transliteration of ฅ kho khon, ฒ tho phuthao and ษ so bo ruesi.
This implementation transliterates ำ as ả instead of å to avoid ambiguity with the hypothetical Thai script sequence ะํ (sara a, nikkhahit).
The ICU implementation transliterates ฯ paiyannoi as ‡ (double dagger) and angkhankhu as || (two ASCII vertical bars).
As the ICU implementation uses Unicode, it cannot reliably distinguish angkhandiao from paiyannoi without a semantic analysis, and makes no such attempt.
(Most Thai input methods ensure that the marks are stored in bottom to top order.)