Penang-style "char koay teow’ is somehow very difficult to emulate outside Penang - I’d been in Kuala Lumpur for 5 years already - it’s only 350km from Penang - but genuine-tasting Penang “char koay teow” is almost impossible to find: only two places in KL did it well - a stall in Hutong foodcourt at Lot 10 in downtown KL, and Penang One, a popular eatery in Bandar Puteri Puchong on the outskirts of KL. The rest all ended up with a “KL-fied” version of the dish which is closer to the version back in China.
Ditto Singapore where I spent most of my life - Singapore-style “char koay teow” has very strong Hokkien influences and the fat rice noodles (“koay teow”) will be mixed with yellow Hokkien noodles and fried together. Dark, sweet soysauce and a blend of salty dark soysauce and light soysauce will be used to give the finished dish a darker hue and slightly sweet-savoury flavour.
Singapore-style “char koay teow” is also lard-heavy & contain cockles, eggs and beansprouts, but it also contained slivered pork (which Penang “char koay teow” don’t use), but do not use Chinese sausages nor chives. It’s also gluggier than Penang “char koay teow” as water will be added at the end of the frying process and the whole mixture will be slightly mushed up (very Hokkien-style), whereas Penang “char koay teow” has a lighter appearance.
Some places in Singapore will claim to serve Penang-style “char koay teow” but will inadvertently end up with something in-between the Penang and Singapore versions. I’d never found real Penang “char koay teow” in more than 4 decades in Singapore 
Mary Yeoh and her husband, Yeoh Teng Chye, who own/run Sedap are from Penang, so they “should” know the authentic version. It’s hard to replicate in their kitchen, though - genuine Penang “char koay teow” is seared over very high charcoal flames, uses a lot of lard, and is usually plated on banana leaves.
My visits to Sedap yielded some of the best Malaysian/Singaporean food I’d had in London, but nothing tasted 100% authentic - inadvertently, the tastes and textures have been tweaked to suit the London palate.
