It really depends upon the individual restaurant and how important authenticity is to them.
Pasta ( typically used for spaghetti) is made from durum wheat.
Lo Mein noodles are egg noodles. That’s what authentic type restaurants use.
The quickie cheapo hole in the wall takeouts typically found in many urban areas usually use the cheapest ingredients ( spaghetti noodles) and pre-made sauces purchased in huge containers.
White cloth sit-down Asian restaurants obviously cost more and typically use authentic ingredients such as real Chinese Lo Mein (egg) noodles and sauces individually made for each dish.
I’ve eaten at restaurants of both types and I really don’t care whether they use pasta or authentic Chinese noodles for either Lo Mein or Chow Mein.
But I definitely care about the type of sauce used. There is such a world of difference between the bottled stuff and that made with fresh ingredients.
But in some dishes like Chow Fun there just is no substitute for the freshly made wide rice noodles which are essential to the dish. Thats why relatively few restaurants have it on the menu. But it does tend to make a handy litmus test for authenticity :)
If a restaurant is going to offer Chow Fun requiring authentic rice noodles, chances are that the rest of their ingredients are likewise authentic.