Curtilage Listed?

[Planning Novice]

I have 2 questions, please:

1. Is it an absolute requirement that an ancillary building (cottage), sold into new ownership, must have been part of the same title of the Grade II listed building (farmhouse) AT THE TIME IT WAS LISTED in order to be caught by the listing rules? Or can other factors, in aggregate, be taken into account?

The two properties were under common ownership for all periods (earliest map I can find is 1870s) up until about 10 years before the Farmhouse was listed.

The properties are separated by only approx 5 metres, with a post and rail fence in between.

The properties are accessed via a shared driveway, and share the same name (pointing to link in historic function).
 

2. In the above scenario, the LB sold land (no structures) to the owner of the Cottage 15 years AFTER the listing.

The land now serves as the garden to the Cottage. Respective gardens are separated by a post and rails fence. 

Assuming (subject to answer to Q1) the listing rules will not apply to the Cottage as the conveyance occurred prior to the listing, would the listing rules apply to the garden? 

Thank you.