Hello : )
Where did you get him?
The last time I questioned a collector about an Engineering Pilot, I ate crow, then we became good friends and eventually I helped him get his figures authenticated as Engineering Pilots by matching hand writing samples to my own EP's.
But there is a big BUT here, that other collector found his in a verified find from a former Kenner Employee. That's why I ask where you got him. EP's are mostly production figures, the very end of the line for pre-production that have numbers usually under their feet. Although I did have a first shot Lando with huge number "2" on his back. With all that said, a lot of times, kids would write initials, or numbers, or symbols to distinguish them apart from other friend's figures. EP's have to have provenance to prove they came from a Kenner source, otherwise they are just looked at as another production figure. One other sign of it being an EP would be if it is incomplete, missing a sticker, paint ect... also extra flashing around legs and under feet...
Hope this helps and sorry for my book. When you have a chance let me/us know where you got your Fett.