I'm not sure that I've knowingly ever seen a 40 year old Meserve Holly. How big is that fella? Has it ever been pruned? If that plant is still alive, photos of it would be an awesome contribution to the Database. A documentary of its life and "offspring" would make a great article for the Holly Society Journal - I could steer you to appropriate contacts in that regard.
With that additional information, here are two possible scenarios.
1. Somewhere along the time line from initial propagation of the offspring but before the time you moved the one, that original propagule didn't survive and someone (your dad?) replaced it with a purchased female plant - unbeknownst to you.
2. My initial thoughts before you provided further information...it is well-known and not that uncommon for growers/nurserymen to plant a male and female clone of hollies in the same container or field-grown site. This guarantees that both required partners in pollination are present. If this was the situation in your case, you could have layered both male and female branches from the initial installation.
This is why seeing images of flowers is important. It is easy to tell a male holly flower from a female holly flower - the presence of stamens designate the male flower, and the large central green "bump" of the ovary designate the female flower. Examination of all the plants during flowering should yield some answers, although not necessarily a definitive solution to exactly how you arrived at this situation.
