i work at the Nct but im not repersenting them here (im just a lowly inspector). The E mark can be on the inner or outer sidewall, in fact on some tyres with the "outside" part facing correctly towords the outside, you will find the e mark on the inner sidewall. So this is not a major issue, as us "Nct crowd" do inspect all sides of your tyre to ensure its structure is sound and complies to the rules.
I have found very few tyres without an e mark, with the Chineese rubbish such as Sunny,Wanlai ect theese seem to mostly have an e mark but its a lottery tbh...there are also a few Goodyear Eagle NCT, and F1's going around that have "made in china" on them and theese have presented without the mark, however the ones made elsewhere such as Thailand/Poland do have the mark....also some Bridgestones have made their way here without the mark....but basicaly, why not leave it up to the NCT to inspect them, thats our job, and please bear in mind that a re-inspection on your tyres is free if its found that they dont have the mark, even despite the rubbish you will hear on Joe Duffy ect ect..