I appreciate the confusion that the rules may cause so hopefully I can clarify.
You must be a member of the ABCA to run in either Finals. You need to be a member of the USBCHA to run in a trial to qualify but you do not need to be an ABCA member just to qualify. However, you must join prior to running. Your dog must be registered with the ABCA only to receive ABCA prize money. A non-registered dog may run, and win; it just doesn't get as much prize money.
Under Part I of the Rules, which applies to both Sheep and Cattle Finals, it states the following:
Members must be in good standing to earn points towards participation in the USBCHA Open Finals and qualifying legs for the USBCHA Nursery Finals. To participate in the USBCHA National Finals, one must also be a member in good standing of the American Border Collie Association (ABCA).
Part IV.C (which are the cattle rules) are not inconsistent. It states that you must be a USBCHA member to receive qualification and then comply with the Rules (which includes Part I).
This could certainly be more clear and I will suggest that we include the membership language for the finals in both Part III (sheepdog finals) and Part IV (cattle dog finals).
The reason for this is that the ABCA is our partner in both Finals, contributing significant funds. Neither Finals would happen without the ABCA's sponsorship and partnership. As far as I know, this has been the rule for some time, but I obviously haven't been around that long.
I hope this helps, and I will take this opportunity to once again thank the ABCA for its generous support.