Late and borderline are not the same
A sign is thirty degrees wide and the last face covers a third of it, so being in that face says only that you are in the closing stretch. The question of whether a boundary is reachable depends on how many degrees remain and how far the date drifts between years.
Here about three and a half degrees remain at the top of the range, which is over three days of solar motion, against an annual spread of a degree and a bit. The arithmetic does not permit a Cancer answer on this date in any year sampled from 1930 to 2035.
What the last face does affect is the reading offered by the decan tables, and those apply to the whole ten degree band without regard to how close the sign boundary is. Late in the face and early in it are treated alike by both schemes.
What a cusp actually means
At any instant the Sun occupies one longitude, and that longitude is inside exactly one sign. There is no zone in which it is partly in two. What people call a cusp is a description of missing information: a year, an hour or a birthplace that has not been supplied.
On dates where the boundary genuinely falls within the day, supplying those details settles the matter. On this date there is nothing to settle, because no combination of hour and time zone moves the Sun anywhere near ninety degrees of longitude.
The dates where the word does real work are few, and they cluster on the two or three days each month when a boundary can fall on either side of noon. For those, a year, an hour and a place settle the question outright, and the blend disappears.
The position and its face
Twenty six degrees falls in the last face of Gemini, which starts at twenty. The Chaldean order gives that band to the Sun and the triplicity count reads it as the Aquarius portion of the sign, handing it to Saturn, or to Uranus in modern usage.
Mercury rules Gemini throughout, and the face is a subdivision within that rule rather than a competing claim. Both schemes are traditional attributions, recorded here as such, and a source quoting one ought to say which it is using.
What is genuinely open
The Moon is the real variable on a 17 June birth. It moves about thirteen degrees a day, so it will be in one of two signs and the hour decides, and its sign changes a reading far more than the choice of decan ruler does.
The ascendant is open across all twelve signs and depends on latitude as well as clock time. The widget above computes the solar degree from your own year, hour and place and states the distance to the nearest boundary, which is what a cusp claim would need in order to stand up.
Houses are open as well, and they depend on the same two details. Until they are supplied the Sun on 17 June has a sign, a degree and a face, which is a good deal more than most pages offer and a good deal less than a chart.
Questions people ask about this
Am I a Gemini Cancer cusp if I was born on 17 June?
No. Three days or so of Gemini remain at this point, and no birth hour or time zone crosses that gap. The Sun was in Gemini in every year sampled at noon from 1930 to 2035.
Is there such a thing as a cusp at all?
Not as a mixed state. The Sun has one longitude at a time and it lies in one sign. The word describes uncertainty in the information rather than a condition of the chart.
What degree is the Sun on 17 June?
Around twenty six degrees of Gemini, with a range of roughly twenty five point four to twenty six point seven at noon across the years checked.
When does Gemini actually end?
At the June solstice, when the Sun reaches ninety degrees of longitude. That falls on the twentieth or twenty first in the years sampled.
Which decan is 17 June in?
The third face of Gemini, twenty degrees onward, ruled by the Sun in the Chaldean order and by Saturn through Aquarius in the triplicity scheme.
Does a late degree carry any special meaning?
Some practitioners treat the final degrees of a sign as its most concentrated expression, and others attach nothing to them. It is interpretation either way, and the measurable fact is simply the position.