Did alll engine lids have Porsche letters on them

Nope

Andy would know what years and why? I would think first two years?

Wasn't it North America had letters, EU didn't as they were sold as VW-Porsche?

It is my understanding that Porsche letters were only installed on 914’s sold thru Porsche dealers in the USA and possibly Canada. No letters on the engine lid grills for 914s sold in the rest of the world as VW-Porsches.