I was looking at the ringed spots on the forewing which seem atypical for the Hackberry. Do they can vary a lot from individual to individual?

The Kaufman field guide (1) shows 3 variations, and only 1 distinctly shows eyespots. I'm not sure if these forms are seasonal variations, but I'm pretty sure I've seen a couple in my area so they must not be geographical variations.

There is a lot of variation in the eye spots on the front wings of A. celtis. There are regional trends in how many spots there are, but there is often quite a lot of variation between individuals in the same population too. There is often a difference between top and bottom sides of the wing too. There may be only one, near the lower outer angle of the wing (tornus), or there may be two there, those two may be a partial or complete ring, or even solid black (the upper one is most varied, and usually least developed of the two). Up at the angle in the outer margin of the wing just below the tip of the wing, the second (sometimes it is the third) white spots down (the offset one) is often ringed too - as in this photo. Occasionally there is a hint of blue in the center of one or more of these eye spots (but this is more common on the hind wing). Rarely, the spot in between is ringed too, making four in a row. So, there can be one to four, and sometimes even a bare trace of a fifth below all these. It is very very rare indeed that there are no eye spots on the front wing, but that is the common condition in A. clyton. In A. leilia the eye spots are much as in A. celtis, except the lower two are more consistent, pretty much always present, and the upper one near the angle in the wing is often almost entirely dark, with the white barely showing. A. clyton can rarely have one or two of these eye spots at least partially developed too, so you have to look at other pattern elements too, such as the bars across the discal cell and the shape of the dark lines across the middle of the wing.

Lots of good info there...