I am pretty sure the 25ES100 has different optical prescription (lense count, surface radii) than the others in the 2" *ES100 line.
Well, this is also true of the TeleVue Ethos line, with lens counts from 8 to 10, and the Pentax XW line with lens counts from 6 to 8.
But we still consider them part of a line because they were designed to have similar optical characteristics.
In the case of the 25, many of its parameters (like eye relief) and aberrations are simply an extrapolation of the shorter focal lengths.
Even its weight is a simple extension of the 20mm.
That makes it a part of the family rather than a stand-alone design like the 9mm 120°.