In reply to Simon&Jim:
Thanks for your feedback.
As far as we are aware, this is an old restriction on the buttress La Cantera with the popular route La Cantera (5c). It is covered in the current book and Rockfax Digital for the two routes it relates to. Looking at UKC logbooks, we have some ascents in April and March pre-dating the 2013 edition of the book which was our first book to include the restriction, but none since then, so it appears people are respecting it.
If anyone has an update to this then please let us know.
Alan
Post edited at 10:47