A isol 1 not decomposed, when A isol 3 is

[r12a]

If i understand correctly, to represent isolated form no. 3 per the chart in section 1.2.2 of the graphetic model description, one has to use two graphetic characters, ie.

equals

+

Yet to represent

one can do so with a single character, rather than using

+

Is that correct? And if so, why the discrepancy?

[lianghai]

A.1.isol's toothless-left-tail (zero tooth) is simply an incidental feature of the tooth/cap when a tooth/cap ends a sequence but can't expand to a normal right-tail (one tooth), eg, a tooth on an isol position or on a fina position preceded by a round consonant (B, feminine G, etc).

One can only use the single tooth graphetic character to produce a shape like A.1.isol or E.1.isol. For modern Hudum there isn't a character for the jointed toothless-left-tail in the graphetic approach. The last image in your message is a non-joining character only used for the disjointed tail (čačulg_a / tsatslag) which is encoded in the current encoding.