The oldest arms you refer to are not Masterson arms, they are a derivative of the Mainwaring otherwise the Mannering family. These are mentioned in Burkes general Amory. Given the intermarriage between the Masterson and Mainwaring families, it is likely that information passed on to Burke was incorrect, probably coming from some quartering of both family's arms. .
I just found your channel! So interesting!! I hope one day I can see something our my surname.. Grimaldi !
The oldest arms you refer to are not Masterson arms, they are a derivative of the Mainwaring otherwise the Mannering family. These are mentioned in Burkes general Amory. Given the intermarriage between the Masterson and Mainwaring families, it is likely that information passed on to Burke was incorrect, probably coming from some quartering of both family's arms. .
Plus the family were already had the 3 garbs or before Flodden