Stocking parts purchased from eBay this is not something new.
This is a quick test of what you get from ten L7806CV (LM7806A) priced a 1 Euro shipped.
Max output voltage was delivered with input of 12.5 V.
1_ 6.010
2_ 5.944
3_ 5.911
4_ 5.926
5_ 5.932
6_ 5.964
7_ 5.920
8_ 5.955
9_ 5.943
10_ 5.950
All product samples they have printing L8706CV - CCOKJ - V6 MAR 1718 (with very blurry ST electronics logo at lower left corner).
My quick conclusion this is that all ten are functional and that according to this series electrical specifications, they are in compliance.
Now speaking of specifications with such parts, input voltage should never be lower than 8.5V if you aim stabilization in a wide range of load.
I do consider use of heatsink as absolutely necessary especially when input voltage this is above 20V.