Surely your experience sheets of the logbook should be signed by the person who either 1/. Signed off the rectification task that you were assigned to assist with / do (Must be a "B"), or 2/. be the covering "B" supervisor for the "A" Tech you were helping. They are stating that you have done/been involved in those tasks.
The Competencies (that I assume you are really refering to), should be signed by a person assigned as an assessor by the company MOE (as you have found out). Surely, your assesors should be able to determine if you have reached those competenies by looking at your experience sheets and questioning you about those tasks and the relevent facets.. True, I know of assessors in my company that want to see you put in every crimp, bolt, rivet, before they sign, including a good grilling on the subject!
The chapter 2 in my book for example has lots of stamps from various LAEs from my first company worked for (as a connie). I was never made aware of OJT assessors in that company (but as a connie did they care?) My permie job has seen a couple of non OJT assesor LAEs sign it (they didn't know about the company position either!) but since I found out, I only use the specified names.. Might be a problem with quality, but if they cannot accept that a 25 year time ex forces guy with several years proven experience in a 145 enviroment is competent, I'm in the wrong industry!!