Technically there are under-barrel markings. The matter is discussed in Roger Rule's seminal work "The Rifleman's Rifle". If you can't get a positive answer here, you should be able to obtain a copy of the Rule book through "Interlibrary Loan".
Yet there is another reality too. It's broader than just the Supergrade family. "It's the poorly concealed dark little secret of 'mix n' match'likely impacting much of the Pre-64 Model 70 design. Many as we see them today are mix-masters from the so-called 'all original guns they once were. Yet in most instances, if 'well stirred, not shaken'
the point with humor, never to know. Far more than a few Supergrades will not exhibit such as the internal markings. Real Supergrades or not? Nowadays, if it quacks like a duck... That the mentality. Better that it otherwise look all original and pristine too if possible! There are a number of characteristics comprising the true Supergrade, but I fear only to a purist, the under-barrel markings required. Otherwise the 'essential' Supergrade more likely encountered.
So am I deferring on your question? Actually 'fudging'. Unequivocally... Yes! Get a copy of the Rule book and view the nuances. Yet the market has largely decided to ignore such markings. It's cast the decisive vote in most instances, for the cleanest, most original 'appearing' rifle consonant with 'not rocking the collector boat'. If all the visible ducks line up well and the condition is good; all else to be shoved aside
This is absolutely just my take and more a feature of the realistic situation I perceive. Others may differ.
Just my take!