Jorge wrote: I thought that since the female families are all tidily numbered that they were more strict in keeping those lineages uninterrupted, you know, from a "tail-female" lineage perspective.
Can you share a little more on the rules they are applying today?
Pasting in from the ISBC's website
http://www.horseracingintfed.com/aboutDisplay.asp?section=10&file=5
Promotion of Mares and Stallions to Vehicle Status - it is important for good order that all Stud Books should have a common approach to the eligibility of evolving bloodlines. Thoroughbred status is achieved after 8 successive crosses of thoroughbred blood and the produce of the seventh cross, if accepted by ISBC, is designated a "vehicle" mare/stallion. The ISBC is the acknowledged authority which can grant this status which is then recognised worldwide.
The produce/progeny of the vehicle mare/stallion is eligible for registration as TB if by/out of a TB recorded in an ISBC member's registry.
And, btw, there are a few TB female lines still active and producing blacktype that have not been assigned an alpha-numeric designation.