A different attempt of tracing the four missing months.

Conditions:
(1) A08 only contains 4 signs, and not 5.
(2) The northern or southern area contains an 18th thorn.
Conclusion:
Signs and units are days, signgroups are equal to weeks. 7 or 8 signgroups with alternately 29 or 31 signs are months.

Move the 61th signgroup "A31" into the bull's eye, and unfold the two spirals to a single grand circle, that A30 is followed by B01 and B30 by A01. Such circle has a periphery of 240 signs.
Now displace the starting point from A01 one step back to B30, and count foreward 8 signgroups, accordingly {B30,A01,A02,A03,A04,A05,A06,A07}, and continue with the next 7 signgroups.Make this shift eight times in total for the 61-1 signgroups. A count over will ensure you that each area of 8 and 7 signgroups contains 29 and 31 visible signs by turn! Finally A31.
This was all about the 243 signs which are visible on the Disc in this productive variation of my 244-day prototype calendar.

If you are aware of my interpretation of this hieroglyphic inscription, you'll know that I plead that all signs form part of elements of always two signs. My method thereby determines 70 stem-elements together with 104 incomplete elements, because they only contain a single sign. In other words the inscription is in lack of 104 units. The same figure as the number of reduced elements.
Prototype: 70 x2 stem-elements and 104 incomplete elements consequently 104 absent units, plus 17 strokes.
Variation : 70 x2 stem-elements and 103 reduced elements consequently 103 invisible units, plus 18 thorns

Imagine a compass card being placed in the middle of the grand-circle, appointing {B30,A01,A02,A03,A04,A05,A06,A07}as the western area, and {A30,B01,B02,B03,B04,B05,B06,B07} as the eastern area. The signgroups in those two corners contain together 31 reduced stems or 31 absent units (if you can possess something absent.) The same pattern repeats itself for the 8 northern and 8 southern signgroups, while it is somehow different with the 7 signgroups sited northwest and the 7 in southwest with 29 units together, and finally for the northeast and southeast signgroups with 29 unit-days, thus forming a fleur-de-lis. As to symmetry, not unlike the pointer figure of the various Maya and Actez calendar stones.
This was my introduction to the missing season of the Phaistos Disc Calendar.

The Phaistos disc alias the Minoan calendar