do you have chapter & verse for the regulation that requires an Instructor to countersign the entry you intend to use for Reval by Experience?
AMC1 FCL.050 instruction time:
(4) instruction time: a summary of all time logged by an applicant for a licence or rating as flight instruction, instrument flight instruction, instrument ground time, etc., may be logged if certified by the appropriately rated or authorised instructor from whom it was received;