Doctor seems to be used for the seventh child in the family though this does not always follow. Another naming amusement is using the surname as the first name my line goes back to Pickup Pickup, and there are a few in the area in the 81c. Doctor crops up a few times in our line which as been traced, by Craig and Albert Pickup, back to James Pickup who married Anne Cooper in 1826. It also appears in other Pickup lines. Would be interested in seeing your line.